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/internal/service/routing_cache.go

@@ -8,6 +8,7 @@ import (
 
 	"nex/backend/internal/domain"
 	"nex/backend/internal/repository"
+	pkglogger "nex/backend/pkg/logger"
 )
 
 type RoutingCache struct {
@@ -27,7 +28,7 @@ func NewRoutingCache(
 	return &RoutingCache{
 		modelRepo:    modelRepo,
 		providerRepo: providerRepo,
-		logger:       logger,
+		logger:       pkglogger.WithModule(logger, "service.routing_cache"),
 	}
 }
 

backend/internal/service/service_supplemental_test.go

@@ -5,6 +5,7 @@ import (
 
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
+	"go.uber.org/zap"
 
 	"nex/backend/internal/domain"
 	"nex/backend/internal/repository"
@@ -119,7 +120,7 @@ func TestModelService_Delete_NotFound(t *testing.T) {
 
 func TestStatsService_Aggregate_Default(t *testing.T) {
 	statsRepo := repository.NewStatsRepository(nil)
-	buffer := NewStatsBuffer(statsRepo, nil)
+	buffer := NewStatsBuffer(statsRepo, zap.NewNop())
 	svc := NewStatsService(statsRepo, buffer)
 
 	stats := []domain.UsageStats{

backend/internal/service/service_test.go

@@ -318,7 +318,7 @@ func TestStatsService_Aggregate_ByModel(t *testing.T) {
 		t.Run(tt.name, func(t *testing.T) {
 			db := setupServiceTestDB(t)
 			statsRepo := repository.NewStatsRepository(db)
-			buffer := NewStatsBuffer(statsRepo, nil); svc := NewStatsService(statsRepo, buffer)
+			buffer := NewStatsBuffer(statsRepo, zap.NewNop()); svc := NewStatsService(statsRepo, buffer)
 
 			result := svc.Aggregate(tt.stats, "model")
 
@@ -379,7 +379,7 @@ func TestStatsService_Aggregate_ByDate(t *testing.T) {
 		t.Run(tt.name, func(t *testing.T) {
 			db := setupServiceTestDB(t)
 			statsRepo := repository.NewStatsRepository(db)
-			buffer := NewStatsBuffer(statsRepo, nil); svc := NewStatsService(statsRepo, buffer)
+			buffer := NewStatsBuffer(statsRepo, zap.NewNop()); svc := NewStatsService(statsRepo, buffer)
 
 			result := svc.Aggregate(tt.stats, "date")
 

backend/internal/service/stats_buffer.go

@@ -9,6 +9,7 @@ import (
 	"go.uber.org/zap"
 
 	"nex/backend/internal/repository"
+	pkglogger "nex/backend/pkg/logger"
 )
 
 type StatsBuffer struct {
@@ -46,7 +47,7 @@ func NewStatsBuffer(
 ) *StatsBuffer {
 	b := &StatsBuffer{
 		statsRepo:      statsRepo,
-		logger:         logger,
+		logger:         pkglogger.WithModule(logger, "service.stats_buffer"),
 		flushInterval:  5 * time.Second,
 		flushThreshold: 100,
 		stopCh:         make(chan struct{}),