fix(backend): 修复 golangci-lint 报告的问题

- gofmt: 修复代码格式问题
- errcheck: 处理 WriteString 和 Close 返回值
- staticcheck: 错误信息改为小写开头
- staticcheck: 移除无效的 nil 检查
- staticcheck: 使用 append 替换循环
- staticcheck: 使用无条件的 TrimPrefix
- ineffassign: 移除无效赋值
- unused: 移除未使用的 geminiOAuthService 字段
- 重新生成 wire_gen.go

backend/internal/config/config.go

@@ -221,10 +221,10 @@ func setDefaults() {
 
 	// TokenRefresh
 	viper.SetDefault("token_refresh.enabled", true)
-	viper.SetDefault("token_refresh.check_interval_minutes", 5)       // 每5分钟检查一次
+	viper.SetDefault("token_refresh.check_interval_minutes", 5)        // 每5分钟检查一次
 	viper.SetDefault("token_refresh.refresh_before_expiry_hours", 0.5) // 提前30分钟刷新（适配Google 1小时token）
-	viper.SetDefault("token_refresh.max_retries", 3)                  // 最多重试3次
-	viper.SetDefault("token_refresh.retry_backoff_seconds", 2)        // 重试退避基础2秒
+	viper.SetDefault("token_refresh.max_retries", 3)                   // 最多重试3次
+	viper.SetDefault("token_refresh.retry_backoff_seconds", 2)         // 重试退避基础2秒
 
 	// Gemini OAuth - configure via environment variables or config file
 	// GEMINI_OAUTH_CLIENT_ID and GEMINI_OAUTH_CLIENT_SECRET

backend/internal/pkg/geminicli/models.go

@@ -19,4 +19,3 @@ var DefaultModels = []Model{
 
 // DefaultTestModel is the default model to preselect in test flows.
 const DefaultTestModel = "gemini-2.5-pro"
-

backend/internal/pkg/geminicli/oauth.go

@@ -152,7 +152,7 @@ func EffectiveOAuthConfig(cfg OAuthConfig, oauthType string) (OAuthConfig, error
 
 	// Require OAuth credentials to be configured
 	if effective.ClientID == "" || effective.ClientSecret == "" {
-		return OAuthConfig{}, fmt.Errorf("Gemini OAuth credentials not configured. Set GEMINI_OAUTH_CLIENT_ID and GEMINI_OAUTH_CLIENT_SECRET environment variables")
+		return OAuthConfig{}, fmt.Errorf("gemini OAuth credentials not configured, set GEMINI_OAUTH_CLIENT_ID and GEMINI_OAUTH_CLIENT_SECRET environment variables")
 	}
 
 	if effective.Scopes == "" {

backend/internal/pkg/googleapi/status.go

@@ -22,4 +22,3 @@ func HTTPStatusToGoogleStatus(status int) string {
 		return "UNKNOWN"
 	}
 }
-

backend/internal/service/account_test_service.go

@@ -43,7 +43,6 @@ type AccountTestService struct {
 	accountRepo         AccountRepository
 	oauthService        *OAuthService
 	openaiOAuthService  *OpenAIOAuthService
-	geminiOAuthService  *GeminiOAuthService
 	geminiTokenProvider *GeminiTokenProvider
 	httpUpstream        HTTPUpstream
 }
@@ -53,7 +52,6 @@ func NewAccountTestService(
 	accountRepo AccountRepository,
 	oauthService *OAuthService,
 	openaiOAuthService *OpenAIOAuthService,
-	geminiOAuthService *GeminiOAuthService,
 	geminiTokenProvider *GeminiTokenProvider,
 	httpUpstream HTTPUpstream,
 ) *AccountTestService {
@@ -61,7 +59,6 @@ func NewAccountTestService(
 		accountRepo:         accountRepo,
 		oauthService:        oauthService,
 		openaiOAuthService:  openaiOAuthService,
-		geminiOAuthService:  geminiOAuthService,
 		geminiTokenProvider: geminiTokenProvider,
 		httpUpstream:        httpUpstream,
 	}
@@ -460,7 +457,7 @@ func (s *AccountTestService) testGeminiAccountConnection(c *gin.Context, account
 func (s *AccountTestService) buildGeminiAPIKeyRequest(ctx context.Context, account *model.Account, modelID string, payload []byte) (*http.Request, error) {
 	apiKey := account.GetCredential("api_key")
 	if strings.TrimSpace(apiKey) == "" {
-		return nil, fmt.Errorf("No API key available")
+		return nil, fmt.Errorf("no API key available")
 	}
 
 	baseURL := account.GetCredential("base_url")
@@ -486,13 +483,13 @@ func (s *AccountTestService) buildGeminiAPIKeyRequest(ctx context.Context, accou
 // buildGeminiOAuthRequest builds request for Gemini OAuth accounts
 func (s *AccountTestService) buildGeminiOAuthRequest(ctx context.Context, account *model.Account, modelID string, payload []byte) (*http.Request, error) {
 	if s.geminiTokenProvider == nil {
-		return nil, fmt.Errorf("Gemini token provider not configured")
+		return nil, fmt.Errorf("gemini token provider not configured")
 	}
 
 	// Get access token (auto-refreshes if needed)
 	accessToken, err := s.geminiTokenProvider.GetAccessToken(ctx, account)
 	if err != nil {
-		return nil, fmt.Errorf("Failed to get access token: %w", err)
+		return nil, fmt.Errorf("failed to get access token: %w", err)
 	}
 
 	projectID := strings.TrimSpace(account.GetCredential("project_id"))

backend/internal/service/gemini_messages_compat_service.go

@@ -365,10 +365,6 @@ func (s *GeminiMessagesCompatService) Forward(ctx context.Context, c *gin.Contex
 		return nil, fmt.Errorf("unsupported account type: %s", account.Type)
 	}
 
-	if buildReq == nil {
-		return nil, s.writeClaudeError(c, http.StatusBadGateway, "upstream_error", "Gemini upstream not configured")
-	}
-
 	var resp *http.Response
 	for attempt := 1; attempt <= geminiMaxRetries; attempt++ {
 		upstreamReq, idHeader, err := buildReq(ctx)
@@ -1128,7 +1124,6 @@ func (s *GeminiMessagesCompatService) handleStreamingResponse(c *gin.Context, re
 						"index": openToolIndex,
 					})
 					openToolIndex = -1
-					openToolID = ""
 					openToolName = ""
 					seenToolJSON = ""
 				}
@@ -2069,7 +2064,7 @@ func extractClaudeContentText(v any) string {
 			}
 			if pm["type"] == "text" {
 				if text, ok := pm["text"].(string); ok {
-					sb.WriteString(text)
+					_, _ = sb.WriteString(text)
 				}
 			}
 		}

backend/internal/service/gemini_oauth_service.go

@@ -436,7 +436,7 @@ func fetchProjectIDFromResourceManager(ctx context.Context, accessToken, proxyUR
 	if err != nil {
 		return "", fmt.Errorf("resource manager request failed: %w", err)
 	}
-	defer resp.Body.Close()
+	defer func() { _ = resp.Body.Close() }()
 
 	bodyBytes, err := io.ReadAll(resp.Body)
 	if err != nil {

backend/internal/service/pricing_service.go

@@ -445,13 +445,11 @@ func (s *PricingService) buildModelLookupCandidates(modelLower string) []string
 		normalizeModelNameForPricing(modelLower),
 		modelLower,
 	}
-	for _, cand := range []string{
+	candidates = append(candidates,
 		strings.TrimPrefix(modelLower, "models/"),
 		lastSegment(modelLower),
 		lastSegment(strings.TrimPrefix(modelLower, "models/")),
-	} {
-		candidates = append(candidates, cand)
-	}
+	)
 
 	seen := make(map[string]struct{}, len(candidates))
 	out := make([]string, 0, len(candidates))
@@ -479,13 +477,8 @@ func normalizeModelNameForPricing(model string) string {
 	// - projects/.../locations/.../publishers/google/models/gemini-1.5-pro
 	model = strings.TrimSpace(model)
 	model = strings.TrimLeft(model, "/")
-
-	if strings.HasPrefix(model, "models/") {
-		model = strings.TrimPrefix(model, "models/")
-	}
-	if strings.HasPrefix(model, "publishers/google/models/") {
-		model = strings.TrimPrefix(model, "publishers/google/models/")
-	}
+	model = strings.TrimPrefix(model, "models/")
+	model = strings.TrimPrefix(model, "publishers/google/models/")
 
 	if idx := strings.LastIndex(model, "/publishers/google/models/"); idx != -1 {
 		model = model[idx+len("/publishers/google/models/"):]