fix: 修复代码审查报告中的4个关键问题

1. 资源管理冗余（ForwardGemini双重Close）
   - 错误分支读取body后立即关闭原始body，用内存副本重新包装
   - defer添加nil guard，避免重复关闭
   - fallback成功时显式关闭旧body，确保连接释放

2. Schema校验丢失（cleanJSONSchema移除字段无感知）
   - 新增schemaCleaningWarningsEnabled()支持环境变量控制
   - 实现warnSchemaKeyRemovedOnce()在非release模式下告警
   - 移除关键验证字段时输出warning，包含key和path

3. UI响应式风险（UsersView操作菜单硬编码定位）
   - 菜单改为先粗定位、渲染后测量、再clamp到视口内
   - 添加max-height + overflow-auto，超出时可滚动
   - 增强交互：点击其它位置/滚动/resize自动关闭或重新定位

4. 身份补丁干扰（TransformClaudeToGemini默认注入）
   - 新增TransformOptions + TransformClaudeToGeminiWithOptions
   - 系统设置新增enable_identity_patch、identity_patch_prompt
   - 完整打通handler/dto/service/frontend配置链路
   - 默认保持启用，向后兼容现有行为

测试：
- 后端单测全量通过：go test ./...
- 前端类型检查通过：npm run typecheck

backend/internal/service/antigravity_gateway_service.go

@@ -255,6 +255,16 @@ func (s *AntigravityGatewayService) buildClaudeTestRequest(projectID, mappedMode
 	return antigravity.TransformClaudeToGemini(claudeReq, projectID, mappedModel)
 }
 
+func (s *AntigravityGatewayService) getClaudeTransformOptions(ctx context.Context) antigravity.TransformOptions {
+	opts := antigravity.DefaultTransformOptions()
+	if s.settingService == nil {
+		return opts
+	}
+	opts.EnableIdentityPatch = s.settingService.IsIdentityPatchEnabled(ctx)
+	opts.IdentityPatch = s.settingService.GetIdentityPatchPrompt(ctx)
+	return opts
+}
+
 // extractGeminiResponseText 从 Gemini 响应中提取文本
 func extractGeminiResponseText(respBody []byte) string {
 	var resp map[string]any
@@ -380,7 +390,7 @@ func (s *AntigravityGatewayService) Forward(ctx context.Context, c *gin.Context,
 	}
 
 	// 转换 Claude 请求为 Gemini 格式
-	geminiBody, err := antigravity.TransformClaudeToGemini(&claudeReq, projectID, mappedModel)
+	geminiBody, err := antigravity.TransformClaudeToGeminiWithOptions(&claudeReq, projectID, mappedModel, s.getClaudeTransformOptions(ctx))
 	if err != nil {
 		return nil, fmt.Errorf("transform request: %w", err)
 	}
@@ -466,7 +476,7 @@ func (s *AntigravityGatewayService) Forward(ctx context.Context, c *gin.Context,
 
 				log.Printf("Antigravity account %d: detected signature-related 400, retrying once (%s)", account.ID, stage.name)
 
-				retryGeminiBody, txErr := antigravity.TransformClaudeToGemini(&retryClaudeReq, projectID, mappedModel)
+				retryGeminiBody, txErr := antigravity.TransformClaudeToGeminiWithOptions(&retryClaudeReq, projectID, mappedModel, s.getClaudeTransformOptions(ctx))
 				if txErr != nil {
 					continue
 				}

backend/internal/service/domain_constants.go

@@ -101,6 +101,10 @@ const (
 	SettingKeyFallbackModelOpenAI      = "fallback_model_openai"
 	SettingKeyFallbackModelGemini      = "fallback_model_gemini"
 	SettingKeyFallbackModelAntigravity = "fallback_model_antigravity"
+
+	// Request identity patch (Claude -> Gemini systemInstruction injection)
+	SettingKeyEnableIdentityPatch = "enable_identity_patch"
+	SettingKeyIdentityPatchPrompt = "identity_patch_prompt"
 )
 
 // AdminAPIKeyPrefix is the prefix for admin API keys (distinct from user "sk-" keys).

backend/internal/service/setting_service.go

@@ -130,6 +130,10 @@ func (s *SettingService) UpdateSettings(ctx context.Context, settings *SystemSet
 	updates[SettingKeyFallbackModelGemini] = settings.FallbackModelGemini
 	updates[SettingKeyFallbackModelAntigravity] = settings.FallbackModelAntigravity
 
+	// Identity patch configuration (Claude -> Gemini)
+	updates[SettingKeyEnableIdentityPatch] = strconv.FormatBool(settings.EnableIdentityPatch)
+	updates[SettingKeyIdentityPatchPrompt] = settings.IdentityPatchPrompt
+
 	return s.settingRepo.SetMultiple(ctx, updates)
 }
 
@@ -213,6 +217,9 @@ func (s *SettingService) InitializeDefaultSettings(ctx context.Context) error {
 		SettingKeyFallbackModelOpenAI:      "gpt-4o",
 		SettingKeyFallbackModelGemini:      "gemini-2.5-pro",
 		SettingKeyFallbackModelAntigravity: "gemini-2.5-pro",
+		// Identity patch defaults
+		SettingKeyEnableIdentityPatch: "true",
+		SettingKeyIdentityPatchPrompt: "",
 	}
 
 	return s.settingRepo.SetMultiple(ctx, defaults)
@@ -269,6 +276,14 @@ func (s *SettingService) parseSettings(settings map[string]string) *SystemSettin
 	result.FallbackModelGemini = s.getStringOrDefault(settings, SettingKeyFallbackModelGemini, "gemini-2.5-pro")
 	result.FallbackModelAntigravity = s.getStringOrDefault(settings, SettingKeyFallbackModelAntigravity, "gemini-2.5-pro")
 
+	// Identity patch settings (default: enabled, to preserve existing behavior)
+	if v, ok := settings[SettingKeyEnableIdentityPatch]; ok && v != "" {
+		result.EnableIdentityPatch = v == "true"
+	} else {
+		result.EnableIdentityPatch = true
+	}
+	result.IdentityPatchPrompt = settings[SettingKeyIdentityPatchPrompt]
+
 	return result
 }
 
@@ -298,6 +313,25 @@ func (s *SettingService) GetTurnstileSecretKey(ctx context.Context) string {
 	return value
 }
 
+// IsIdentityPatchEnabled 检查是否启用身份补丁（Claude -> Gemini systemInstruction 注入）
+func (s *SettingService) IsIdentityPatchEnabled(ctx context.Context) bool {
+	value, err := s.settingRepo.GetValue(ctx, SettingKeyEnableIdentityPatch)
+	if err != nil {
+		// 默认开启，保持兼容
+		return true
+	}
+	return value == "true"
+}
+
+// GetIdentityPatchPrompt 获取自定义身份补丁提示词（为空表示使用内置默认模板）
+func (s *SettingService) GetIdentityPatchPrompt(ctx context.Context) string {
+	value, err := s.settingRepo.GetValue(ctx, SettingKeyIdentityPatchPrompt)
+	if err != nil {
+		return ""
+	}
+	return value
+}
+
 // GenerateAdminAPIKey 生成新的管理员 API Key
 func (s *SettingService) GenerateAdminAPIKey(ctx context.Context) (string, error) {
 	// 生成 32 字节随机数 = 64 位十六进制字符

backend/internal/service/settings_view.go

@@ -32,6 +32,10 @@ type SystemSettings struct {
 	FallbackModelOpenAI      string `json:"fallback_model_openai"`
 	FallbackModelGemini      string `json:"fallback_model_gemini"`
 	FallbackModelAntigravity string `json:"fallback_model_antigravity"`
+
+	// Identity patch configuration (Claude -> Gemini)
+	EnableIdentityPatch bool   `json:"enable_identity_patch"`
+	IdentityPatchPrompt string `json:"identity_patch_prompt"`
 }
 
 type PublicSettings struct {