fix(lint): 修复 golangci-lint 报告的代码问题

- errcheck: 修复类型断言未检查返回值的问题
  - pool.go: 添加 sync.Map 类型断言安全检查
  - req_client_pool.go: 添加 sync.Map 类型断言安全检查
  - concurrency_cache_benchmark_test.go: 显式忽略断言返回值
  - gateway_service.go: 显式忽略 WriteString 返回值

- gofmt: 修复代码格式问题
  - redis.go: 注释对齐
  - api_key_repo.go: 结构体字段对齐
  - concurrency_cache.go: 字段对齐
  - http_upstream.go: 注释对齐

- unused: 删除未使用的代码
  - user_repo.go: 删除未使用的 sql 字段
  - usage_service.go: 删除未使用的 calculateStats 函数

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/internal/pkg/httpclient/pool.go

@@ -58,7 +58,9 @@ var sharedClients sync.Map
 func GetClient(opts Options) (*http.Client, error) {
 	key := buildClientKey(opts)
 	if cached, ok := sharedClients.Load(key); ok {
-		return cached.(*http.Client), nil
+		if client, ok := cached.(*http.Client); ok {
+			return client, nil
+		}
 	}
 
 	client, err := buildClient(opts)
@@ -72,7 +74,10 @@ func GetClient(opts Options) (*http.Client, error) {
 	}
 
 	actual, _ := sharedClients.LoadOrStore(key, client)
-	return actual.(*http.Client), nil
+	if c, ok := actual.(*http.Client); ok {
+		return c, nil
+	}
+	return client, nil
 }
 
 func buildClient(opts Options) (*http.Client, error) {

backend/internal/repository/concurrency_cache_benchmark_test.go

@@ -22,7 +22,7 @@ func BenchmarkAccountConcurrency(b *testing.B) {
 		_ = rdb.Close()
 	}()
 
-	cache := NewConcurrencyCache(rdb, benchSlotTTLMinutes).(*concurrencyCache)
+	cache, _ := NewConcurrencyCache(rdb, benchSlotTTLMinutes).(*concurrencyCache)
 	ctx := context.Background()
 
 	for _, size := range []int{10, 100, 1000} {

backend/internal/repository/req_client_pool.go

@@ -35,7 +35,9 @@ var sharedReqClients sync.Map
 func getSharedReqClient(opts reqClientOptions) *req.Client {
 	key := buildReqClientKey(opts)
 	if cached, ok := sharedReqClients.Load(key); ok {
-		return cached.(*req.Client)
+		if c, ok := cached.(*req.Client); ok {
+			return c
+		}
 	}
 
 	client := req.C().SetTimeout(opts.Timeout)
@@ -47,7 +49,10 @@ func getSharedReqClient(opts reqClientOptions) *req.Client {
 	}
 
 	actual, _ := sharedReqClients.LoadOrStore(key, client)
-	return actual.(*req.Client)
+	if c, ok := actual.(*req.Client); ok {
+		return c
+	}
+	return client
 }
 
 func buildReqClientKey(opts reqClientOptions) string {

backend/internal/repository/user_repo.go

@@ -16,15 +16,14 @@ import (
 
 type userRepository struct {
 	client *dbent.Client
-	sql    sqlExecutor
 }
 
 func NewUserRepository(client *dbent.Client, sqlDB *sql.DB) service.UserRepository {
 	return newUserRepositoryWithSQL(client, sqlDB)
 }
 
-func newUserRepositoryWithSQL(client *dbent.Client, sqlq sqlExecutor) *userRepository {
+func newUserRepositoryWithSQL(client *dbent.Client, _ sqlExecutor) *userRepository {
-	return &userRepository{client: client, sql: sqlq}
+	return &userRepository{client: client}
 }
 
 func (r *userRepository) Create(ctx context.Context, userIn *service.User) error {

backend/internal/service/gateway_service.go

@@ -197,7 +197,7 @@ func (s *GatewayService) extractCacheableContent(parsed *ParsedRequest) string {
 				if cc, ok := partMap["cache_control"].(map[string]any); ok {
 					if cc["type"] == "ephemeral" {
 						if text, ok := partMap["text"].(string); ok {
-							builder.WriteString(text)
+							_, _ = builder.WriteString(text)
 						}
 					}
 				}

backend/internal/service/usage_service.go

@@ -235,32 +235,6 @@ func (s *UsageService) GetDailyStats(ctx context.Context, userID int64, days int
 	return stats, nil
 }
 
-// calculateStats 计算统计数据
-func (s *UsageService) calculateStats(logs []UsageLog) *UsageStats {
-	stats := &UsageStats{}
-
-	for _, log := range logs {
-		stats.TotalRequests++
-		stats.TotalInputTokens += int64(log.InputTokens)
-		stats.TotalOutputTokens += int64(log.OutputTokens)
-		stats.TotalCacheTokens += int64(log.CacheCreationTokens + log.CacheReadTokens)
-		stats.TotalTokens += int64(log.TotalTokens())
-		stats.TotalCost += log.TotalCost
-		stats.TotalActualCost += log.ActualCost
-
-		if log.DurationMs != nil {
-			stats.AverageDurationMs += float64(*log.DurationMs)
-		}
-	}
-
-	// 计算平均持续时间
-	if stats.TotalRequests > 0 {
-		stats.AverageDurationMs /= float64(stats.TotalRequests)
-	}
-
-	return stats
-}
-
 // Delete 删除使用日志（管理员功能，谨慎使用）
 func (s *UsageService) Delete(ctx context.Context, id int64) error {
 	if err := s.usageRepo.Delete(ctx, id); err != nil {