feat: add max_claude_code_version setting and disable auto-upgrade env var

Add maximum Claude Code version limit to complement the existing minimum
version check. Refactor the version cache from single-value to unified
bounds struct (min+max) with a single atomic.Value and singleflight group.

- Backend: new constant, struct field, cache refactor, validation (semver
  format + cross-validation max >= min), gateway enforcement, audit diff
- Frontend: settings UI input, TypeScript types, zh/en i18n
- Add CLAUDE_CODE_DISABLE_NONESSENTIAL_TRAFFIC=1 to all Claude Code
  tutorials on /keys page (unix/cmd/powershell/vscode settings.json)

backend/internal/handler/admin/setting_handler.go

@@ -125,6 +125,7 @@ func (h *SettingHandler) GetSettings(c *gin.Context) {
 		OpsQueryModeDefault:                  settings.OpsQueryModeDefault,
 		OpsMetricsIntervalSeconds:            settings.OpsMetricsIntervalSeconds,
 		MinClaudeCodeVersion:                 settings.MinClaudeCodeVersion,
+		MaxClaudeCodeVersion:                 settings.MaxClaudeCodeVersion,
 		AllowUngroupedKeyScheduling:          settings.AllowUngroupedKeyScheduling,
 		BackendModeEnabled:                   settings.BackendModeEnabled,
 	})
@@ -199,6 +200,7 @@ type UpdateSettingsRequest struct {
 	OpsMetricsIntervalSeconds    *int    `json:"ops_metrics_interval_seconds"`
 
 	MinClaudeCodeVersion string `json:"min_claude_code_version"`
+	MaxClaudeCodeVersion string `json:"max_claude_code_version"`
 
 	// 分组隔离
 	AllowUngroupedKeyScheduling bool `json:"allow_ungrouped_key_scheduling"`
@@ -442,6 +444,22 @@ func (h *SettingHandler) UpdateSettings(c *gin.Context) {
 		}
 	}
 
+	// 验证最高版本号格式（空字符串=禁用，或合法 semver）
+	if req.MaxClaudeCodeVersion != "" {
+		if !semverPattern.MatchString(req.MaxClaudeCodeVersion) {
+			response.Error(c, http.StatusBadRequest, "max_claude_code_version must be empty or a valid semver (e.g. 3.0.0)")
+			return
+		}
+	}
+
+	// 交叉验证：如果同时设置了最低和最高版本号，最高版本号必须 >= 最低版本号
+	if req.MinClaudeCodeVersion != "" && req.MaxClaudeCodeVersion != "" {
+		if service.CompareVersions(req.MaxClaudeCodeVersion, req.MinClaudeCodeVersion) < 0 {
+			response.Error(c, http.StatusBadRequest, "max_claude_code_version must be greater than or equal to min_claude_code_version")
+			return
+		}
+	}
+
 	settings := &service.SystemSettings{
 		RegistrationEnabled:              req.RegistrationEnabled,
 		EmailVerifyEnabled:               req.EmailVerifyEnabled,
@@ -488,6 +506,7 @@ func (h *SettingHandler) UpdateSettings(c *gin.Context) {
 		EnableIdentityPatch:              req.EnableIdentityPatch,
 		IdentityPatchPrompt:              req.IdentityPatchPrompt,
 		MinClaudeCodeVersion:             req.MinClaudeCodeVersion,
+		MaxClaudeCodeVersion:             req.MaxClaudeCodeVersion,
 		AllowUngroupedKeyScheduling:      req.AllowUngroupedKeyScheduling,
 		BackendModeEnabled:               req.BackendModeEnabled,
 		OpsMonitoringEnabled: func() bool {
@@ -588,6 +607,7 @@ func (h *SettingHandler) UpdateSettings(c *gin.Context) {
 		OpsQueryModeDefault:                  updatedSettings.OpsQueryModeDefault,
 		OpsMetricsIntervalSeconds:            updatedSettings.OpsMetricsIntervalSeconds,
 		MinClaudeCodeVersion:                 updatedSettings.MinClaudeCodeVersion,
+		MaxClaudeCodeVersion:                 updatedSettings.MaxClaudeCodeVersion,
 		AllowUngroupedKeyScheduling:          updatedSettings.AllowUngroupedKeyScheduling,
 		BackendModeEnabled:                   updatedSettings.BackendModeEnabled,
 	})
@@ -744,6 +764,9 @@ func diffSettings(before *service.SystemSettings, after *service.SystemSettings,
 	if before.MinClaudeCodeVersion != after.MinClaudeCodeVersion {
 		changed = append(changed, "min_claude_code_version")
 	}
+	if before.MaxClaudeCodeVersion != after.MaxClaudeCodeVersion {
+		changed = append(changed, "max_claude_code_version")
+	}
 	if before.AllowUngroupedKeyScheduling != after.AllowUngroupedKeyScheduling {
 		changed = append(changed, "allow_ungrouped_key_scheduling")
 	}

backend/internal/handler/dto/settings.go

@@ -79,6 +79,7 @@ type SystemSettings struct {
 	OpsMetricsIntervalSeconds    int    `json:"ops_metrics_interval_seconds"`
 
 	MinClaudeCodeVersion string `json:"min_claude_code_version"`
+	MaxClaudeCodeVersion string `json:"max_claude_code_version"`
 
 	// 分组隔离
 	AllowUngroupedKeyScheduling bool `json:"allow_ungrouped_key_scheduling"`

backend/internal/handler/gateway_handler.go

@@ -1281,7 +1281,7 @@ func (h *GatewayHandler) ensureForwardErrorResponse(c *gin.Context, streamStarte
 	return true
 }
 
-// checkClaudeCodeVersion 检查 Claude Code 客户端版本是否满足最低要求
+// checkClaudeCodeVersion 检查 Claude Code 客户端版本是否满足版本要求
 // 仅对已识别的 Claude Code 客户端执行，count_tokens 路径除外
 func (h *GatewayHandler) checkClaudeCodeVersion(c *gin.Context) bool {
 	ctx := c.Request.Context()
@@ -1294,8 +1294,8 @@ func (h *GatewayHandler) checkClaudeCodeVersion(c *gin.Context) bool {
 		return true
 	}
 
-	minVersion := h.settingService.GetMinClaudeCodeVersion(ctx)
-	if minVersion == "" {
+	minVersion, maxVersion := h.settingService.GetClaudeCodeVersionBounds(ctx)
+	if minVersion == "" && maxVersion == "" {
 		return true // 未设置，不检查
 	}
 
@@ -1306,13 +1306,22 @@ func (h *GatewayHandler) checkClaudeCodeVersion(c *gin.Context) bool {
 		return false
 	}
 
-	if service.CompareVersions(clientVersion, minVersion) < 0 {
+	if minVersion != "" && service.CompareVersions(clientVersion, minVersion) < 0 {
 		h.errorResponse(c, http.StatusBadRequest, "invalid_request_error",
 			fmt.Sprintf("Your Claude Code version (%s) is below the minimum required version (%s). Please update: npm update -g @anthropic-ai/claude-code",
 				clientVersion, minVersion))
 		return false
 	}
 
+	if maxVersion != "" && service.CompareVersions(clientVersion, maxVersion) > 0 {
+		h.errorResponse(c, http.StatusBadRequest, "invalid_request_error",
+			fmt.Sprintf("Your Claude Code version (%s) exceeds the maximum allowed version (%s). "+
+				"Please downgrade: npm install -g @anthropic-ai/claude-code@%s && "+
+				"set CLAUDE_CODE_DISABLE_NONESSENTIAL_TRAFFIC=1 to prevent auto-upgrade",
+				clientVersion, maxVersion, maxVersion))
+		return false
+	}
+
 	return true
 }