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/handler/provider_handler.go

@@ -2,19 +2,25 @@ package handler
 
 import (
 	"net/http"
+	"strings"
 
 	"github.com/gin-gonic/gin"
 	"gorm.io/gorm"
 
-	"nex/backend/internal/config"
+	appErrors "nex/backend/pkg/errors"
+
+	"nex/backend/internal/domain"
+	"nex/backend/internal/service"
 )
 
 // ProviderHandler 供应商管理处理器
-type ProviderHandler struct{}
+type ProviderHandler struct {
+	providerService service.ProviderService
+}
 
 // NewProviderHandler 创建供应商处理器
-func NewProviderHandler() *ProviderHandler {
-	return &ProviderHandler{}
+func NewProviderHandler(providerService service.ProviderService) *ProviderHandler {
+	return &ProviderHandler{providerService: providerService}
 }
 
 // CreateProvider 创建供应商
@@ -33,43 +39,34 @@ func (h *ProviderHandler) CreateProvider(c *gin.Context) {
 		return
 	}
 
-	// 创建供应商对象
-	provider := &config.Provider{
+	provider := &domain.Provider{
 		ID:      req.ID,
 		Name:    req.Name,
 		APIKey:  req.APIKey,
 		BaseURL: req.BaseURL,
-		Enabled: true, // 默认启用
 	}
 
-	// 保存到数据库
-	err := config.CreateProvider(provider)
+	err := h.providerService.Create(provider)
 	if err != nil {
-		// 检查是否是唯一约束错误（ID 重复）
-		if err.Error() == "UNIQUE constraint failed: providers.id" {
+		if strings.Contains(err.Error(), "UNIQUE constraint failed") {
 			c.JSON(http.StatusConflict, gin.H{
 				"error": "供应商 ID 已存在",
 			})
 			return
 		}
-		c.JSON(http.StatusInternalServerError, gin.H{
-			"error": "创建供应商失败: " + err.Error(),
-		})
+		writeError(c, err)
 		return
 	}
 
-	// 掩码 API Key 后返回
 	provider.MaskAPIKey()
 	c.JSON(http.StatusCreated, provider)
 }
 
 // ListProviders 列出所有供应商
 func (h *ProviderHandler) ListProviders(c *gin.Context) {
-	providers, err := config.ListProviders()
+	providers, err := h.providerService.List()
 	if err != nil {
-		c.JSON(http.StatusInternalServerError, gin.H{
-			"error": "查询供应商失败: " + err.Error(),
-		})
+		writeError(c, err)
 		return
 	}
 
@@ -80,7 +77,7 @@ func (h *ProviderHandler) ListProviders(c *gin.Context) {
 func (h *ProviderHandler) GetProvider(c *gin.Context) {
 	id := c.Param("id")
 
-	provider, err := config.GetProvider(id, true) // 掩码 API Key
+	provider, err := h.providerService.Get(id, true)
 	if err != nil {
 		if err == gorm.ErrRecordNotFound {
 			c.JSON(http.StatusNotFound, gin.H{
@@ -88,9 +85,7 @@ func (h *ProviderHandler) GetProvider(c *gin.Context) {
 			})
 			return
 		}
-		c.JSON(http.StatusInternalServerError, gin.H{
-			"error": "查询供应商失败: " + err.Error(),
-		})
+		writeError(c, err)
 		return
 	}
 
@@ -109,8 +104,7 @@ func (h *ProviderHandler) UpdateProvider(c *gin.Context) {
 		return
 	}
 
-	// 更新供应商
-	err := config.UpdateProvider(id, req)
+	err := h.providerService.Update(id, req)
 	if err != nil {
 		if err == gorm.ErrRecordNotFound {
 			c.JSON(http.StatusNotFound, gin.H{
@@ -118,18 +112,13 @@ func (h *ProviderHandler) UpdateProvider(c *gin.Context) {
 			})
 			return
 		}
-		c.JSON(http.StatusInternalServerError, gin.H{
-			"error": "更新供应商失败: " + err.Error(),
-		})
+		writeError(c, err)
 		return
 	}
 
-	// 返回更新后的供应商
-	provider, err := config.GetProvider(id, true)
+	provider, err := h.providerService.Get(id, true)
 	if err != nil {
-		c.JSON(http.StatusInternalServerError, gin.H{
-			"error": "查询更新后的供应商失败: " + err.Error(),
-		})
+		writeError(c, err)
 		return
 	}
 
@@ -140,8 +129,7 @@ func (h *ProviderHandler) UpdateProvider(c *gin.Context) {
 func (h *ProviderHandler) DeleteProvider(c *gin.Context) {
 	id := c.Param("id")
 
-	// 删除供应商（级联删除模型）
-	err := config.DeleteProvider(id)
+	err := h.providerService.Delete(id)
 	if err != nil {
 		if err == gorm.ErrRecordNotFound {
 			c.JSON(http.StatusNotFound, gin.H{
@@ -149,19 +137,23 @@ func (h *ProviderHandler) DeleteProvider(c *gin.Context) {
 			})
 			return
 		}
-		c.JSON(http.StatusInternalServerError, gin.H{
-			"error": "删除供应商失败: " + err.Error(),
-		})
+		writeError(c, err)
 		return
 	}
 
-	// 删除关联的模型
-	models, _ := config.ListModels("")
-	for _, model := range models {
-		if model.ProviderID == id {
-			_ = config.DeleteModel(model.ID)
-		}
-	}
-
 	c.Status(http.StatusNoContent)
 }
+
+// writeError 统一错误响应处理
+func writeError(c *gin.Context, err error) {
+	if appErr, ok := appErrors.AsAppError(err); ok {
+		c.JSON(appErr.HTTPStatus, gin.H{
+			"error": appErr.Message,
+			"code":  appErr.Code,
+		})
+		return
+	}
+	c.JSON(http.StatusInternalServerError, gin.H{
+		"error": err.Error(),
+	})
+}