feat: 实现统一模型 ID 机制

实现统一模型 ID 格式 (provider_id/model_name)，支持跨协议模型标识和 Smart Passthrough。

核心变更：
- 新增 pkg/modelid 包：解析、格式化、校验统一模型 ID
- 数据库迁移：models 表使用 UUID 主键 + UNIQUE(provider_id, model_name) 约束
- Repository 层：FindByProviderAndModelName、ListEnabled 方法
- Service 层：联合唯一校验、provider ID 字符集校验
- Conversion 层：ExtractModelName、RewriteRequestModelName/RewriteResponseModelName 方法
- Handler 层：统一模型 ID 路由、Smart Passthrough、Models API 本地聚合
- 新增 error-responses、unified-model-id 规范

测试覆盖：
- 单元测试：modelid、conversion、handler、service、repository
- 集成测试：统一模型 ID 路由、Smart Passthrough 保真性、跨协议转换
- 迁移测试：UUID 主键、UNIQUE 约束、级联删除

OpenSpec：
- 归档 unified-model-id 变更到 archive/2026-04-21-unified-model-id
- 同步 11 个 delta specs 到 main specs
- 新增 error-responses、unified-model-id 规范文件

backend/pkg/errors/errors.go

@@ -49,17 +49,20 @@ func NewAppError(code, message string, httpStatus int) *AppError {
 
 // Predefined errors
 var (
-	ErrModelNotFound    = NewAppError("model_not_found", "模型未找到", http.StatusNotFound)
-	ErrModelDisabled    = NewAppError("model_disabled", "模型已禁用", http.StatusNotFound)
-	ErrProviderNotFound = NewAppError("provider_not_found", "供应商未找到", http.StatusNotFound)
-	ErrProviderDisabled = NewAppError("provider_disabled", "供应商已禁用", http.StatusNotFound)
-	ErrInvalidRequest   = NewAppError("invalid_request", "无效的请求", http.StatusBadRequest)
-	ErrInternal         = NewAppError("internal_error", "内部错误", http.StatusInternalServerError)
-	ErrDatabaseNotInit  = NewAppError("database_not_initialized", "数据库未初始化", http.StatusInternalServerError)
-	ErrConflict         = NewAppError("conflict", "资源已存在", http.StatusConflict)
-	ErrRequestCreate    = NewAppError("request_create_error", "创建请求失败", http.StatusInternalServerError)
-	ErrRequestSend      = NewAppError("request_send_error", "发送请求失败", http.StatusBadGateway)
-	ErrResponseRead     = NewAppError("response_read_error", "读取响应失败", http.StatusBadGateway)
+	ErrModelNotFound     = NewAppError("model_not_found", "模型未找到", http.StatusNotFound)
+	ErrModelDisabled     = NewAppError("model_disabled", "模型已禁用", http.StatusNotFound)
+	ErrProviderNotFound  = NewAppError("provider_not_found", "供应商未找到", http.StatusNotFound)
+	ErrProviderDisabled  = NewAppError("provider_disabled", "供应商已禁用", http.StatusNotFound)
+	ErrInvalidRequest    = NewAppError("invalid_request", "无效的请求", http.StatusBadRequest)
+	ErrInternal          = NewAppError("internal_error", "内部错误", http.StatusInternalServerError)
+	ErrDatabaseNotInit   = NewAppError("database_not_initialized", "数据库未初始化", http.StatusInternalServerError)
+	ErrConflict          = NewAppError("conflict", "资源已存在", http.StatusConflict)
+	ErrRequestCreate     = NewAppError("request_create_error", "创建请求失败", http.StatusInternalServerError)
+	ErrRequestSend       = NewAppError("request_send_error", "发送请求失败", http.StatusBadGateway)
+	ErrResponseRead      = NewAppError("response_read_error", "读取响应失败", http.StatusBadGateway)
+	ErrInvalidProviderID = NewAppError("invalid_provider_id", "供应商 ID 仅允许字母、数字、下划线，长度 1-64", http.StatusBadRequest)
+	ErrDuplicateModel    = NewAppError("duplicate_model", "同一供应商下模型名称已存在", http.StatusConflict)
+	ErrImmutableField    = NewAppError("immutable_field", "供应商 ID 不允许修改", http.StatusBadRequest)
 )
 
 // AsAppError 尝试将 error 转换为 *AppError

backend/pkg/logger/logger.go

@@ -9,6 +9,14 @@ import (
 	"go.uber.org/zap/zapcore"
 )
 
+// stdoutWriter 包装 os.Stdout，忽略 Sync() 错误。
+// 在非 TTY 环境（如 go test）中，os.Stdout 被重定向为 pipe，
+// 底层 fsync 会返回 "bad file descriptor"。zap 社区标准做法。
+type stdoutWriter struct{}
+
+func (stdoutWriter) Write(p []byte) (int, error) { return os.Stdout.Write(p) }
+func (stdoutWriter) Sync() error                 { return nil }
+
 // Config 日志配置
 type Config struct {
 	Level      string // 日志级别: debug, info, warn, error
@@ -46,7 +54,7 @@ func New(cfg Config) (*zap.Logger, error) {
 
 	stdoutCore := zapcore.NewCore(
 		stdoutEncoder,
-		zapcore.AddSync(os.Stdout),
+		zapcore.AddSync(stdoutWriter{}),
 		level,
 	)
 

backend/pkg/modelid/model_id.go

@@ -0,0 +1,63 @@
+package modelid
+
+import (
+	"errors"
+	"regexp"
+	"strings"
+)
+
+var providerIDRegex = regexp.MustCompile(`^[a-zA-Z0-9_]+$`)
+
+// ParseUnifiedModelID 将 "provider_id/model_name" 格式的字符串解析为 providerID 和 modelName
+// 在第一个 "/" 处分割，model_name 可以包含 "/"
+func ParseUnifiedModelID(id string) (providerID, modelName string, err error) {
+	if id == "" {
+		return "", "", errors.New("统一模型 ID 不能为空")
+	}
+
+	parts := strings.SplitN(id, "/", 2)
+	if len(parts) != 2 {
+		return "", "", errors.New("统一模型 ID 格式错误，缺少分隔符 \"/\"")
+	}
+
+	providerID = parts[0]
+	modelName = parts[1]
+
+	if providerID == "" {
+		return "", "", errors.New("provider_id 不能为空")
+	}
+	if modelName == "" {
+		return "", "", errors.New("model_name 不能为空")
+	}
+
+	if !providerIDRegex.MatchString(providerID) {
+		return "", "", errors.New("provider_id 仅允许字母、数字、下划线")
+	}
+
+	return providerID, modelName, nil
+}
+
+// FormatUnifiedModelID 将 providerID 和 modelName 组合格式化为统一模型 ID
+func FormatUnifiedModelID(providerID, modelName string) string {
+	return providerID + "/" + modelName
+}
+
+// ValidateProviderID 校验 providerID 仅包含字母、数字、下划线，长度 1-64
+func ValidateProviderID(id string) error {
+	if id == "" {
+		return errors.New("provider_id 不能为空")
+	}
+	if len(id) > 64 {
+		return errors.New("provider_id 长度不能超过 64 个字符")
+	}
+	if !providerIDRegex.MatchString(id) {
+		return errors.New("provider_id 仅允许字母、数字、下划线")
+	}
+	return nil
+}
+
+// IsValidUnifiedModelID 判断字符串是否为合法的统一模型 ID 格式
+func IsValidUnifiedModelID(id string) bool {
+	_, _, err := ParseUnifiedModelID(id)
+	return err == nil
+}

backend/pkg/modelid/model_id_test.go

@@ -0,0 +1,96 @@
+package modelid
+
+import (
+	"strings"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestParseUnifiedModelID_StandardFormat(t *testing.T) {
+	providerID, modelName, err := ParseUnifiedModelID("openai/gpt-4")
+	assert.NoError(t, err)
+	assert.Equal(t, "openai", providerID)
+	assert.Equal(t, "gpt-4", modelName)
+}
+
+func TestParseUnifiedModelID_ModelNameWithSlashes(t *testing.T) {
+	providerID, modelName, err := ParseUnifiedModelID("azure/accounts/org-123/models/gpt-4")
+	assert.NoError(t, err)
+	assert.Equal(t, "azure", providerID)
+	assert.Equal(t, "accounts/org-123/models/gpt-4", modelName)
+}
+
+func TestParseUnifiedModelID_MissingSeparator(t *testing.T) {
+	_, _, err := ParseUnifiedModelID("gpt-4")
+	assert.Error(t, err)
+}
+
+func TestParseUnifiedModelID_EmptyString(t *testing.T) {
+	_, _, err := ParseUnifiedModelID("")
+	assert.Error(t, err)
+}
+
+func TestParseUnifiedModelID_OnlySeparator(t *testing.T) {
+	tests := []string{"/model", "provider/", "/"}
+	for _, tc := range tests {
+		_, _, err := ParseUnifiedModelID(tc)
+		assert.Error(t, err, "输入 %q 应返回错误", tc)
+	}
+}
+
+func TestParseUnifiedModelID_InvalidProviderID(t *testing.T) {
+	tests := []string{
+		"open-ai/gpt-4",
+		"open.ai/gpt-4",
+		"供应商/gpt-4",
+		"open ai/gpt-4",
+	}
+	for _, tc := range tests {
+		_, _, err := ParseUnifiedModelID(tc)
+		assert.Error(t, err, "providerID 含非法字符 %q 应返回错误", tc)
+	}
+}
+
+func TestFormatUnifiedModelID(t *testing.T) {
+	assert.Equal(t, "openai/gpt-4", FormatUnifiedModelID("openai", "gpt-4"))
+	assert.Equal(t, "anthropic/claude-3-opus", FormatUnifiedModelID("anthropic", "claude-3-opus"))
+}
+
+func TestValidateProviderID_Valid(t *testing.T) {
+	validIDs := []string{"openai", "deep_seek", "provider01", "OpenAI"}
+	for _, id := range validIDs {
+		assert.NoError(t, ValidateProviderID(id), "%q 应校验通过", id)
+	}
+}
+
+func TestValidateProviderID_InvalidChars(t *testing.T) {
+	invalidIDs := []string{"open-ai", "open.ai", "open ai", "供应商", "open/ai"}
+	for _, id := range invalidIDs {
+		assert.Error(t, ValidateProviderID(id), "%q 应校验失败", id)
+	}
+}
+
+func TestValidateProviderID_Empty(t *testing.T) {
+	assert.Error(t, ValidateProviderID(""))
+}
+
+func TestValidateProviderID_TooLong(t *testing.T) {
+	longID := strings.Repeat("a", 65)
+	assert.Error(t, ValidateProviderID(longID))
+
+	exactly64 := strings.Repeat("a", 64)
+	assert.NoError(t, ValidateProviderID(exactly64))
+}
+
+func TestIsValidUnifiedModelID(t *testing.T) {
+	assert.True(t, IsValidUnifiedModelID("openai/gpt-4"))
+	assert.True(t, IsValidUnifiedModelID("anthropic/claude-3-opus-20240229"))
+	assert.True(t, IsValidUnifiedModelID("azure/accounts/org/models/gpt-4"))
+
+	assert.False(t, IsValidUnifiedModelID(""))
+	assert.False(t, IsValidUnifiedModelID("gpt-4"))
+	assert.False(t, IsValidUnifiedModelID("open-ai/gpt-4"))
+	assert.False(t, IsValidUnifiedModelID("/model"))
+	assert.False(t, IsValidUnifiedModelID("provider/"))
+}