refactor: 后端日志系统重构

- 新增模块化日志器（pkg/logger/module.go）
- 新增 GORM 日志适配器
- 统一日志入口，移除所有 zap.L() 全局 logger 调用
- 字段标准化
- 启动阶段使用结构化日志
- 更新所有相关测试

backend/cmd/server/main.go

@@ -3,7 +3,6 @@ package main
 import (
 	"context"
 	"fmt"
-	"log"
 	"net/http"
 	"os"
 	"os/signal"
@@ -27,14 +26,14 @@ import (
 )
 
 func main() {
+	minimalLogger := pkgLogger.NewMinimal()
+
 	cfg, err := config.LoadConfig()
 	if err != nil {
-		log.Fatalf("加载配置失败: %v", err)
+		minimalLogger.Fatal("加载配置失败", zap.Error(err))
 	}
 
-	cfg.PrintSummary()
-
-	zapLogger, err := pkgLogger.New(pkgLogger.Config{
+	zapLogger, err := pkgLogger.Upgrade(minimalLogger, pkgLogger.Config{
 		Level:      cfg.Log.Level,
 		Path:       cfg.Log.Path,
 		MaxSize:    cfg.Log.MaxSize,
@@ -43,13 +42,15 @@ func main() {
 		Compress:   cfg.Log.Compress,
 	})
 	if err != nil {
-		log.Fatalf("初始化日志失败: %v", err)
+		minimalLogger.Fatal("初始化日志失败", zap.Error(err))
 	}
 	defer zapLogger.Sync()
 
+	cfg.PrintSummary(zapLogger)
+
 	db, err := database.Init(&cfg.Database, zapLogger)
 	if err != nil {
-		zapLogger.Fatal("初始化数据库失败", zap.String("error", err.Error()))
+		zapLogger.Fatal("初始化数据库失败", zap.Error(err))
 	}
 	defer database.Close(db)
 
@@ -74,16 +75,16 @@ func main() {
 
 	registry := conversion.NewMemoryRegistry()
 	if err := registry.Register(openai.NewAdapter()); err != nil {
-		zapLogger.Fatal("注册 OpenAI 适配器失败", zap.String("error", err.Error()))
+		zapLogger.Fatal("注册 OpenAI 适配器失败", zap.Error(err))
 	}
 	if err := registry.Register(anthropic.NewAdapter()); err != nil {
-		zapLogger.Fatal("注册 Anthropic 适配器失败", zap.String("error", err.Error()))
+		zapLogger.Fatal("注册 Anthropic 适配器失败", zap.Error(err))
 	}
 	engine := conversion.NewConversionEngine(registry, zapLogger)
 
-	providerClient := provider.NewClient()
+	providerClient := provider.NewClient(zapLogger)
 
-	proxyHandler := handler.NewProxyHandler(engine, providerClient, routingService, providerService, statsService)
+	proxyHandler := handler.NewProxyHandler(engine, providerClient, routingService, providerService, statsService, zapLogger)
 	providerHandler := handler.NewProviderHandler(providerService)
 	modelHandler := handler.NewModelHandler(modelService)
 	statsHandler := handler.NewStatsHandler(statsService)
@@ -108,7 +109,7 @@ func main() {
 	go func() {
 		zapLogger.Info("AI Gateway 启动", zap.String("addr", srv.Addr))
 		if err := srv.ListenAndServe(); err != nil && err != http.ErrServerClosed {
-			zapLogger.Fatal("服务器启动失败", zap.String("error", err.Error()))
+			zapLogger.Fatal("服务器启动失败", zap.Error(err))
 		}
 	}()
 
@@ -122,7 +123,7 @@ func main() {
 	defer cancel()
 
 	if err := srv.Shutdown(ctx); err != nil {
-		zapLogger.Fatal("服务器强制关闭", zap.String("error", err.Error()))
+		zapLogger.Fatal("服务器强制关闭", zap.Error(err))
 	}
 
 	statsBuffer.Stop()