fix: resolve CI lint errors and test compilation failures for rate limit feature

- Fix errcheck: properly handle rows.Close() error via named return + defer closure
- Fix gofmt: auto-format billing_cache.go, api_key_service.go, billing_cache_service.go
- Add missing rate limit interface methods to 4 test stubs (GetRateLimitData, IncrementRateLimitUsage, ResetRateLimitWindows)
- Fix NewBillingCacheService calls missing the new apiKeyRepo parameter

backend/internal/handler/gateway_handler_warmup_intercept_unit_test.go

@@ -159,7 +159,7 @@ func newTestGatewayHandler(t *testing.T, group *service.Group, accounts []*servi
 
 	// RunModeSimple：跳过计费检查，避免引入 repo/cache 依赖。
 	cfg := &config.Config{RunMode: config.RunModeSimple}
-	billingCacheSvc := service.NewBillingCacheService(nil, nil, nil, cfg)
+	billingCacheSvc := service.NewBillingCacheService(nil, nil, nil, nil, cfg)
 
 	concurrencySvc := service.NewConcurrencyService(&fakeConcurrencyCache{})
 	concurrencyHelper := NewConcurrencyHelper(concurrencySvc, SSEPingFormatClaude, 0)

backend/internal/handler/sora_client_handler_test.go

@@ -1032,6 +1032,15 @@ func (r *stubAPIKeyRepoForHandler) IncrementQuotaUsed(_ context.Context, _ int64
 func (r *stubAPIKeyRepoForHandler) UpdateLastUsed(context.Context, int64, time.Time) error {
 	return nil
 }
+func (r *stubAPIKeyRepoForHandler) IncrementRateLimitUsage(context.Context, int64, float64) error {
+	return nil
+}
+func (r *stubAPIKeyRepoForHandler) ResetRateLimitWindows(context.Context, int64) error {
+	return nil
+}
+func (r *stubAPIKeyRepoForHandler) GetRateLimitData(context.Context, int64) (*service.APIKeyRateLimitData, error) {
+	return nil, nil
+}
 
 // newTestAPIKeyService 创建测试用的 APIKeyService
 func newTestAPIKeyService(repo *stubAPIKeyRepoForHandler) *service.APIKeyService {

backend/internal/handler/sora_gateway_handler_test.go

@@ -411,7 +411,7 @@ func TestSoraGatewayHandler_ChatCompletions(t *testing.T) {
 	deferredService := service.NewDeferredService(accountRepo, nil, 0)
 	billingService := service.NewBillingService(cfg, nil)
 	concurrencyService := service.NewConcurrencyService(testutil.StubConcurrencyCache{})
-	billingCacheService := service.NewBillingCacheService(nil, nil, nil, cfg)
+	billingCacheService := service.NewBillingCacheService(nil, nil, nil, nil, cfg)
 	t.Cleanup(func() {
 		billingCacheService.Stop()
 	})

backend/internal/repository/api_key_repo.go

@@ -477,7 +477,7 @@ func (r *apiKeyRepository) ResetRateLimitWindows(ctx context.Context, id int64)
 }
 
 // GetRateLimitData returns the current rate limit usage and window start times for an API key.
-func (r *apiKeyRepository) GetRateLimitData(ctx context.Context, id int64) (*service.APIKeyRateLimitData, error) {
+func (r *apiKeyRepository) GetRateLimitData(ctx context.Context, id int64) (result *service.APIKeyRateLimitData, err error) {
 	rows, err := r.sql.QueryContext(ctx, `
 		SELECT usage_5h, usage_1d, usage_7d, window_5h_start, window_1d_start, window_7d_start
 		FROM api_keys
@@ -486,7 +486,11 @@ func (r *apiKeyRepository) GetRateLimitData(ctx context.Context, id int64) (*ser
 	if err != nil {
 		return nil, err
 	}
-	defer rows.Close()
+	defer func() {
+		if closeErr := rows.Close(); closeErr != nil && err == nil {
+			err = closeErr
+		}
+	}()
 	if !rows.Next() {
 		return nil, service.ErrAPIKeyNotFound
 	}

backend/internal/server/api_contract_test.go

@@ -86,6 +86,15 @@ func TestAPIContracts(t *testing.T) {
 					"last_used_at": null,
 					"quota": 0,
 					"quota_used": 0,
+					"rate_limit_5h": 0,
+					"rate_limit_1d": 0,
+					"rate_limit_7d": 0,
+					"usage_5h": 0,
+					"usage_1d": 0,
+					"usage_7d": 0,
+					"window_5h_start": null,
+					"window_1d_start": null,
+					"window_7d_start": null,
 					"expires_at": null,
 					"created_at": "2025-01-02T03:04:05Z",
 					"updated_at": "2025-01-02T03:04:05Z"
@@ -126,6 +135,15 @@ func TestAPIContracts(t *testing.T) {
 							"last_used_at": null,
 							"quota": 0,
 							"quota_used": 0,
+							"rate_limit_5h": 0,
+							"rate_limit_1d": 0,
+							"rate_limit_7d": 0,
+							"usage_5h": 0,
+							"usage_1d": 0,
+							"usage_7d": 0,
+							"window_5h_start": null,
+							"window_1d_start": null,
+							"window_7d_start": null,
 							"expires_at": null,
 							"created_at": "2025-01-02T03:04:05Z",
 							"updated_at": "2025-01-02T03:04:05Z"
@@ -1506,6 +1524,16 @@ func (r *stubApiKeyRepo) UpdateLastUsed(ctx context.Context, id int64, usedAt ti
 	return nil
 }
 
+func (r *stubApiKeyRepo) IncrementRateLimitUsage(ctx context.Context, id int64, cost float64) error {
+	return nil
+}
+func (r *stubApiKeyRepo) ResetRateLimitWindows(ctx context.Context, id int64) error {
+	return nil
+}
+func (r *stubApiKeyRepo) GetRateLimitData(ctx context.Context, id int64) (*service.APIKeyRateLimitData, error) {
+	return nil, nil
+}
+
 type stubUsageLogRepo struct {
 	userLogs map[int64][]service.UsageLog
 }

backend/internal/server/middleware/api_key_auth_test.go

@@ -588,6 +588,16 @@ func (r *stubApiKeyRepo) UpdateLastUsed(ctx context.Context, id int64, usedAt ti
 	return nil
 }
 
+func (r *stubApiKeyRepo) IncrementRateLimitUsage(ctx context.Context, id int64, cost float64) error {
+	return nil
+}
+func (r *stubApiKeyRepo) ResetRateLimitWindows(ctx context.Context, id int64) error {
+	return nil
+}
+func (r *stubApiKeyRepo) GetRateLimitData(ctx context.Context, id int64) (*service.APIKeyRateLimitData, error) {
+	return nil, nil
+}
+
 type stubUserSubscriptionRepo struct {
 	getActive      func(ctx context.Context, userID, groupID int64) (*service.UserSubscription, error)
 	updateStatus   func(ctx context.Context, subscriptionID int64, status string) error

backend/internal/service/admin_service_apikey_test.go

@@ -127,6 +127,15 @@ func (s *apiKeyRepoStubForGroupUpdate) IncrementQuotaUsed(context.Context, int64
 func (s *apiKeyRepoStubForGroupUpdate) UpdateLastUsed(context.Context, int64, time.Time) error {
 	panic("unexpected")
 }
+func (s *apiKeyRepoStubForGroupUpdate) IncrementRateLimitUsage(context.Context, int64, float64) error {
+	panic("unexpected")
+}
+func (s *apiKeyRepoStubForGroupUpdate) ResetRateLimitWindows(context.Context, int64) error {
+	panic("unexpected")
+}
+func (s *apiKeyRepoStubForGroupUpdate) GetRateLimitData(context.Context, int64) (*APIKeyRateLimitData, error) {
+	panic("unexpected")
+}
 
 // groupRepoStubForGroupUpdate implements GroupRepository for AdminUpdateAPIKeyGroupID tests.
 type groupRepoStubForGroupUpdate struct {

backend/internal/service/admin_service_delete_test.go

@@ -348,6 +348,19 @@ func (s *billingCacheStub) InvalidateSubscriptionCache(ctx context.Context, user
 	return nil
 }
 
+func (s *billingCacheStub) GetAPIKeyRateLimit(ctx context.Context, keyID int64) (*APIKeyRateLimitCacheData, error) {
+	panic("unexpected GetAPIKeyRateLimit call")
+}
+func (s *billingCacheStub) SetAPIKeyRateLimit(ctx context.Context, keyID int64, data *APIKeyRateLimitCacheData) error {
+	panic("unexpected SetAPIKeyRateLimit call")
+}
+func (s *billingCacheStub) UpdateAPIKeyRateLimitUsage(ctx context.Context, keyID int64, cost float64) error {
+	panic("unexpected UpdateAPIKeyRateLimitUsage call")
+}
+func (s *billingCacheStub) InvalidateAPIKeyRateLimit(ctx context.Context, keyID int64) error {
+	panic("unexpected InvalidateAPIKeyRateLimit call")
+}
+
 func waitForInvalidations(t *testing.T, ch <-chan subscriptionInvalidateCall, expected int) []subscriptionInvalidateCall {
 	t.Helper()
 	calls := make([]subscriptionInvalidateCall, 0, expected)

backend/internal/service/api_key_service_cache_test.go

@@ -106,6 +106,15 @@ func (s *authRepoStub) IncrementQuotaUsed(ctx context.Context, id int64, amount
 func (s *authRepoStub) UpdateLastUsed(ctx context.Context, id int64, usedAt time.Time) error {
 	panic("unexpected UpdateLastUsed call")
 }
+func (s *authRepoStub) IncrementRateLimitUsage(ctx context.Context, id int64, cost float64) error {
+	panic("unexpected IncrementRateLimitUsage call")
+}
+func (s *authRepoStub) ResetRateLimitWindows(ctx context.Context, id int64) error {
+	panic("unexpected ResetRateLimitWindows call")
+}
+func (s *authRepoStub) GetRateLimitData(ctx context.Context, id int64) (*APIKeyRateLimitData, error) {
+	panic("unexpected GetRateLimitData call")
+}
 
 type authCacheStub struct {
 	getAuthCache   func(ctx context.Context, key string) (*APIKeyAuthCacheEntry, error)

backend/internal/service/api_key_service_delete_test.go

@@ -134,6 +134,18 @@ func (s *apiKeyRepoStub) UpdateLastUsed(ctx context.Context, id int64, usedAt ti
 	return nil
 }
 
+func (s *apiKeyRepoStub) IncrementRateLimitUsage(ctx context.Context, id int64, cost float64) error {
+	panic("unexpected IncrementRateLimitUsage call")
+}
+
+func (s *apiKeyRepoStub) ResetRateLimitWindows(ctx context.Context, id int64) error {
+	panic("unexpected ResetRateLimitWindows call")
+}
+
+func (s *apiKeyRepoStub) GetRateLimitData(ctx context.Context, id int64) (*APIKeyRateLimitData, error) {
+	panic("unexpected GetRateLimitData call")
+}
+
 // apiKeyCacheStub 是 APIKeyCache 接口的测试桩实现。
 // 用于验证删除操作时缓存清理逻辑是否被正确调用。
 //