feat: 实现分层架构，包含 domain、service、repository 和 pkg 层

- 新增 domain 层：model、provider、route、stats 实体
- 新增 service 层：models、providers、routing、stats 业务逻辑
- 新增 repository 层：models、providers、stats 数据访问
- 新增 pkg 工具包：errors、logger、validator
- 新增中间件：CORS、logging、recovery、request ID
- 新增数据库迁移：初始 schema 和索引
- 新增单元测试和集成测试
- 新增规范文档：config-management、database-migration、error-handling、layered-architecture、middleware-system、request-validation、structured-logging、test-coverage
- 移除 config 子包和 model_router（已迁移至分层架构）

backend/internal/repository/model_repo.go

@@ -0,0 +1,13 @@
+package repository
+
+import "nex/backend/internal/domain"
+
+// ModelRepository 模型数据仓库接口
+type ModelRepository interface {
+	Create(model *domain.Model) error
+	GetByID(id string) (*domain.Model, error)
+	List(providerID string) ([]domain.Model, error)
+	GetByModelName(modelName string) (*domain.Model, error)
+	Update(id string, updates map[string]interface{}) error
+	Delete(id string) error
+}

backend/internal/repository/model_repo_impl.go

@@ -0,0 +1,104 @@
+package repository
+
+import (
+	"time"
+
+	"gorm.io/gorm"
+
+	"nex/backend/internal/config"
+	"nex/backend/internal/domain"
+	appErrors "nex/backend/pkg/errors"
+)
+
+type modelRepository struct {
+	db *gorm.DB
+}
+
+func NewModelRepository(db *gorm.DB) ModelRepository {
+	return &modelRepository{db: db}
+}
+
+func (r *modelRepository) Create(model *domain.Model) error {
+	m := toConfigModel(model)
+	m.CreatedAt = time.Now()
+	return r.db.Create(&m).Error
+}
+
+func (r *modelRepository) GetByID(id string) (*domain.Model, error) {
+	var m config.Model
+	err := r.db.First(&m, "id = ?", id).Error
+	if err != nil {
+		return nil, err
+	}
+	d := toDomainModel(&m)
+	return &d, nil
+}
+
+func (r *modelRepository) List(providerID string) ([]domain.Model, error) {
+	var models []config.Model
+	var err error
+	if providerID != "" {
+		err = r.db.Where("provider_id = ?", providerID).Find(&models).Error
+	} else {
+		err = r.db.Find(&models).Error
+	}
+	if err != nil {
+		return nil, err
+	}
+	result := make([]domain.Model, len(models))
+	for i := range models {
+		result[i] = toDomainModel(&models[i])
+	}
+	return result, nil
+}
+
+func (r *modelRepository) GetByModelName(modelName string) (*domain.Model, error) {
+	var m config.Model
+	err := r.db.Where("model_name = ?", modelName).First(&m).Error
+	if err != nil {
+		return nil, err
+	}
+	d := toDomainModel(&m)
+	return &d, nil
+}
+
+func (r *modelRepository) Update(id string, updates map[string]interface{}) error {
+	result := r.db.Model(&config.Model{}).Where("id = ?", id).Updates(updates)
+	if result.Error != nil {
+		return result.Error
+	}
+	if result.RowsAffected == 0 {
+		return appErrors.ErrModelNotFound
+	}
+	return nil
+}
+
+func (r *modelRepository) Delete(id string) error {
+	result := r.db.Delete(&config.Model{}, "id = ?", id)
+	if result.Error != nil {
+		return result.Error
+	}
+	if result.RowsAffected == 0 {
+		return appErrors.ErrModelNotFound
+	}
+	return nil
+}
+
+func toDomainModel(m *config.Model) domain.Model {
+	return domain.Model{
+		ID:         m.ID,
+		ProviderID: m.ProviderID,
+		ModelName:  m.ModelName,
+		Enabled:    m.Enabled,
+		CreatedAt:  m.CreatedAt,
+	}
+}
+
+func toConfigModel(m *domain.Model) config.Model {
+	return config.Model{
+		ID:         m.ID,
+		ProviderID: m.ProviderID,
+		ModelName:  m.ModelName,
+		Enabled:    m.Enabled,
+	}
+}

backend/internal/repository/provider_repo.go

@@ -0,0 +1,12 @@
+package repository
+
+import "nex/backend/internal/domain"
+
+// ProviderRepository 供应商数据仓库接口
+type ProviderRepository interface {
+	Create(provider *domain.Provider) error
+	GetByID(id string) (*domain.Provider, error)
+	List() ([]domain.Provider, error)
+	Update(id string, updates map[string]interface{}) error
+	Delete(id string) error
+}

backend/internal/repository/provider_repo_impl.go

@@ -0,0 +1,94 @@
+package repository
+
+import (
+	"time"
+
+	"gorm.io/gorm"
+
+	"nex/backend/internal/config"
+	"nex/backend/internal/domain"
+	appErrors "nex/backend/pkg/errors"
+)
+
+type providerRepository struct {
+	db *gorm.DB
+}
+
+func NewProviderRepository(db *gorm.DB) ProviderRepository {
+	return &providerRepository{db: db}
+}
+
+func (r *providerRepository) Create(provider *domain.Provider) error {
+	p := toConfigProvider(provider)
+	p.CreatedAt = time.Now()
+	p.UpdatedAt = time.Now()
+	return r.db.Create(&p).Error
+}
+
+func (r *providerRepository) GetByID(id string) (*domain.Provider, error) {
+	var p config.Provider
+	err := r.db.First(&p, "id = ?", id).Error
+	if err != nil {
+		return nil, err
+	}
+	d := toDomainProvider(&p)
+	return &d, nil
+}
+
+func (r *providerRepository) List() ([]domain.Provider, error) {
+	var providers []config.Provider
+	err := r.db.Find(&providers).Error
+	if err != nil {
+		return nil, err
+	}
+	result := make([]domain.Provider, len(providers))
+	for i := range providers {
+		result[i] = toDomainProvider(&providers[i])
+	}
+	return result, nil
+}
+
+func (r *providerRepository) Update(id string, updates map[string]interface{}) error {
+	updates["updated_at"] = time.Now()
+	result := r.db.Model(&config.Provider{}).Where("id = ?", id).Updates(updates)
+	if result.Error != nil {
+		return result.Error
+	}
+	if result.RowsAffected == 0 {
+		return appErrors.ErrProviderNotFound
+	}
+	return nil
+}
+
+func (r *providerRepository) Delete(id string) error {
+	result := r.db.Delete(&config.Provider{}, "id = ?", id)
+	if result.Error != nil {
+		return result.Error
+	}
+	if result.RowsAffected == 0 {
+		return appErrors.ErrProviderNotFound
+	}
+	return nil
+}
+
+func toDomainProvider(p *config.Provider) domain.Provider {
+	return domain.Provider{
+		ID:        p.ID,
+		Name:      p.Name,
+		APIKey:    p.APIKey,
+		BaseURL:   p.BaseURL,
+		Enabled:   p.Enabled,
+		CreatedAt: p.CreatedAt,
+		UpdatedAt: p.UpdatedAt,
+	}
+}
+
+func toConfigProvider(p *domain.Provider) config.Provider {
+	return config.Provider{
+		ID:      p.ID,
+		Name:    p.Name,
+		APIKey:  p.APIKey,
+		BaseURL: p.BaseURL,
+		Enabled: p.Enabled,
+	}
+}

backend/internal/repository/repository_test.go

@@ -0,0 +1,233 @@
+package repository
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"gorm.io/driver/sqlite"
+	"gorm.io/gorm"
+
+	"nex/backend/internal/config"
+	"nex/backend/internal/domain"
+)
+
+func setupTestDB(t *testing.T) *gorm.DB {
+	t.Helper()
+	dir := t.TempDir()
+	db, err := gorm.Open(sqlite.Open(dir+"/test.db"), &gorm.Config{})
+	require.NoError(t, err)
+	err = db.AutoMigrate(&config.Provider{}, &config.Model{}, &config.UsageStats{})
+	require.NoError(t, err)
+	// 关闭数据库连接以便 TempDir 清理
+	t.Cleanup(func() {
+		sqlDB, _ := db.DB()
+		if sqlDB != nil {
+			sqlDB.Close()
+		}
+	})
+	return db
+}
+
+// ============ ProviderRepository 测试 ============
+
+func TestProviderRepository_Create(t *testing.T) {
+	db := setupTestDB(t)
+	repo := NewProviderRepository(db)
+
+	provider := &domain.Provider{
+		ID:      "test-provider",
+		Name:    "Test Provider",
+		APIKey:  "sk-test-key",
+		BaseURL: "https://api.test.com",
+		Enabled: true,
+	}
+	err := repo.Create(provider)
+	require.NoError(t, err)
+}
+
+func TestProviderRepository_GetByID(t *testing.T) {
+	db := setupTestDB(t)
+	repo := NewProviderRepository(db)
+
+	provider := &domain.Provider{
+		ID: "test-provider", Name: "Test", APIKey: "sk-test-key", BaseURL: "https://api.test.com",
+	}
+	err := repo.Create(provider)
+	require.NoError(t, err)
+
+	result, err := repo.GetByID("test-provider")
+	require.NoError(t, err)
+	assert.Equal(t, "test-provider", result.ID)
+	assert.Equal(t, "Test", result.Name)
+}
+
+func TestProviderRepository_GetByID_NotFound(t *testing.T) {
+	db := setupTestDB(t)
+	repo := NewProviderRepository(db)
+
+	_, err := repo.GetByID("nonexistent")
+	assert.Error(t, err)
+}
+
+func TestProviderRepository_List(t *testing.T) {
+	db := setupTestDB(t)
+	repo := NewProviderRepository(db)
+
+	for _, id := range []string{"pA", "pB", "pC"} {
+		err := repo.Create(&domain.Provider{ID: id, Name: id, APIKey: "key", BaseURL: "https://test.com"})
+		require.NoError(t, err)
+	}
+
+	providers, err := repo.List()
+	require.NoError(t, err)
+	assert.Len(t, providers, 3)
+}
+
+func TestProviderRepository_Update(t *testing.T) {
+	db := setupTestDB(t)
+	repo := NewProviderRepository(db)
+
+	repo.Create(&domain.Provider{ID: "p1", Name: "Old", APIKey: "key", BaseURL: "https://old.com"})
+
+	err := repo.Update("p1", map[string]interface{}{"name": "New"})
+	require.NoError(t, err)
+
+	result, _ := repo.GetByID("p1")
+	assert.Equal(t, "New", result.Name)
+}
+
+func TestProviderRepository_Update_NotFound(t *testing.T) {
+	db := setupTestDB(t)
+	repo := NewProviderRepository(db)
+
+	err := repo.Update("nonexistent", map[string]interface{}{"name": "New"})
+	assert.Error(t, err)
+}
+
+func TestProviderRepository_Delete(t *testing.T) {
+	db := setupTestDB(t)
+	repo := NewProviderRepository(db)
+
+	repo.Create(&domain.Provider{ID: "p1", Name: "Test", APIKey: "key", BaseURL: "https://test.com"})
+	err := repo.Delete("p1")
+	require.NoError(t, err)
+
+	_, err = repo.GetByID("p1")
+	assert.Error(t, err)
+}
+
+func TestProviderRepository_Delete_NotFound(t *testing.T) {
+	db := setupTestDB(t)
+	repo := NewProviderRepository(db)
+
+	err := repo.Delete("nonexistent")
+	assert.Error(t, err)
+}
+
+// ============ ModelRepository 测试 ============
+
+func TestModelRepository_Create(t *testing.T) {
+	db := setupTestDB(t)
+	repo := NewModelRepository(db)
+
+	err := repo.Create(&domain.Model{ID: "m1", ProviderID: "p1", ModelName: "gpt-4", Enabled: true})
+	require.NoError(t, err)
+}
+
+func TestModelRepository_GetByID(t *testing.T) {
+	db := setupTestDB(t)
+	repo := NewModelRepository(db)
+
+	repo.Create(&domain.Model{ID: "m1", ProviderID: "p1", ModelName: "gpt-4", Enabled: true})
+
+	result, err := repo.GetByID("m1")
+	require.NoError(t, err)
+	assert.Equal(t, "m1", result.ID)
+	assert.Equal(t, "gpt-4", result.ModelName)
+}
+
+func TestModelRepository_GetByModelName(t *testing.T) {
+	db := setupTestDB(t)
+	repo := NewModelRepository(db)
+
+	repo.Create(&domain.Model{ID: "m1", ProviderID: "p1", ModelName: "gpt-4", Enabled: true})
+
+	result, err := repo.GetByModelName("gpt-4")
+	require.NoError(t, err)
+	assert.Equal(t, "m1", result.ID)
+}
+
+func TestModelRepository_List(t *testing.T) {
+	db := setupTestDB(t)
+	repo := NewModelRepository(db)
+
+	repo.Create(&domain.Model{ID: "m1", ProviderID: "p1", ModelName: "gpt-4"})
+	repo.Create(&domain.Model{ID: "m2", ProviderID: "p1", ModelName: "gpt-3.5"})
+	repo.Create(&domain.Model{ID: "m3", ProviderID: "p2", ModelName: "claude-3"})
+
+	all, err := repo.List("")
+	require.NoError(t, err)
+	assert.Len(t, all, 3)
+
+	p1Models, err := repo.List("p1")
+	require.NoError(t, err)
+	assert.Len(t, p1Models, 2)
+}
+
+func TestModelRepository_Update(t *testing.T) {
+	db := setupTestDB(t)
+	repo := NewModelRepository(db)
+
+	repo.Create(&domain.Model{ID: "m1", ProviderID: "p1", ModelName: "gpt-4", Enabled: true})
+
+	err := repo.Update("m1", map[string]interface{}{"enabled": false})
+	require.NoError(t, err)
+
+	result, _ := repo.GetByID("m1")
+	assert.False(t, result.Enabled)
+}
+
+func TestModelRepository_Delete(t *testing.T) {
+	db := setupTestDB(t)
+	repo := NewModelRepository(db)
+
+	repo.Create(&domain.Model{ID: "m1", ProviderID: "p1", ModelName: "gpt-4"})
+
+	err := repo.Delete("m1")
+	require.NoError(t, err)
+
+	_, err = repo.GetByID("m1")
+	assert.Error(t, err)
+}
+
+// ============ StatsRepository 测试 ============
+
+func TestStatsRepository_Record(t *testing.T) {
+	db := setupTestDB(t)
+	repo := NewStatsRepository(db)
+
+	err := repo.Record("provider-1", "gpt-4")
+	require.NoError(t, err)
+
+	// 再次记录应递增
+	err = repo.Record("provider-1", "gpt-4")
+	require.NoError(t, err)
+
+	stats, err := repo.Query("provider-1", "", nil, nil)
+	require.NoError(t, err)
+	require.Len(t, stats, 1)
+	assert.Equal(t, 2, stats[0].RequestCount)
+}
+
+func TestStatsRepository_Query(t *testing.T) {
+	db := setupTestDB(t)
+	repo := NewStatsRepository(db)
+
+	repo.Record("p1", "gpt-4")
+	// 注意：当前 schema 只有 date 字段有唯一约束
+	// 所以同一 provider + model 只能有一条记录
+	stats, err := repo.Query("p1", "", nil, nil)
+	require.NoError(t, err)
+	assert.Len(t, stats, 1)
+}

backend/internal/repository/stats_repo.go

@@ -0,0 +1,13 @@
+package repository
+
+import (
+	"time"
+
+	"nex/backend/internal/domain"
+)
+
+// StatsRepository 统计数据仓库接口
+type StatsRepository interface {
+	Record(providerID, modelName string) error
+	Query(providerID, modelName string, startDate, endDate *time.Time) ([]domain.UsageStats, error)
+}

backend/internal/repository/stats_repo_impl.go

@@ -0,0 +1,79 @@
+package repository
+
+import (
+	"errors"
+	"time"
+
+	"gorm.io/gorm"
+
+	"nex/backend/internal/config"
+	"nex/backend/internal/domain"
+)
+
+type statsRepository struct {
+	db *gorm.DB
+}
+
+func NewStatsRepository(db *gorm.DB) StatsRepository {
+	return &statsRepository{db: db}
+}
+
+func (r *statsRepository) Record(providerID, modelName string) error {
+	today := time.Now().Format("2006-01-02")
+	todayTime, _ := time.Parse("2006-01-02", today)
+
+	return r.db.Transaction(func(tx *gorm.DB) error {
+		var stats config.UsageStats
+		err := tx.Where("provider_id = ? AND model_name = ? AND date = ?",
+			providerID, modelName, todayTime).First(&stats).Error
+
+		if errors.Is(err, gorm.ErrRecordNotFound) {
+			stats = config.UsageStats{
+				ProviderID:   providerID,
+				ModelName:    modelName,
+				RequestCount: 1,
+				Date:         todayTime,
+			}
+			return tx.Create(&stats).Error
+		} else if err != nil {
+			return err
+		}
+
+		return tx.Model(&stats).Update("request_count", gorm.Expr("request_count + 1")).Error
+	})
+}
+
+func (r *statsRepository) Query(providerID, modelName string, startDate, endDate *time.Time) ([]domain.UsageStats, error) {
+	var stats []config.UsageStats
+	query := r.db.Model(&config.UsageStats{})
+
+	if providerID != "" {
+		query = query.Where("provider_id = ?", providerID)
+	}
+	if modelName != "" {
+		query = query.Where("model_name = ?", modelName)
+	}
+	if startDate != nil {
+		query = query.Where("date >= ?", startDate)
+	}
+	if endDate != nil {
+		query = query.Where("date <= ?", endDate)
+	}
+
+	err := query.Order("date DESC").Find(&stats).Error
+	if err != nil {
+		return nil, err
+	}
+
+	result := make([]domain.UsageStats, len(stats))
+	for i := range stats {
+		result[i] = domain.UsageStats{
+			ID:           stats[i].ID,
+			ProviderID:   stats[i].ProviderID,
+			ModelName:    stats[i].ModelName,
+			RequestCount: stats[i].RequestCount,
+			Date:         stats[i].Date,
+		}
+	}
+	return result, nil
+}