fix: security hardening and architectural improvements for custom menu

1. (Critical) Filter admin-only menu items from public API responses -
   both GetPublicSettings handler and GetPublicSettingsForInjection now
   exclude visibility=admin items, preventing unauthorized access to
   admin menu URLs.

2. (Medium) Validate JSON array structure in sanitizeCustomMenuItemsJSON -
   use json.Unmarshal into []json.RawMessage instead of json.Valid to
   reject non-array JSON values that would cause frontend runtime errors.

3. (Medium) Decouple router from business JSON parsing - move origin
   extraction logic from router.go to SettingService.GetFrameSrcOrigins,
   eliminating direct JSON parsing of custom_menu_items in the routing
   layer.

4. (Low) Restrict custom menu item ID charset to [a-zA-Z0-9_-] via
   regex validation, preventing route-breaking characters like / ? # or
   spaces.

5. (Low) Handle crypto/rand error in generateMenuItemID - return error
   instead of silently ignoring, preventing potential duplicate IDs.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/internal/handler/admin/setting_handler.go

@@ -23,11 +23,16 @@ import (
 // semverPattern 预编译 semver 格式校验正则
 var semverPattern = regexp.MustCompile(`^\d+\.\d+\.\d+$`)
 
+// menuItemIDPattern validates custom menu item IDs: alphanumeric, hyphens, underscores only.
+var menuItemIDPattern = regexp.MustCompile(`^[a-zA-Z0-9_-]+$`)
+
 // generateMenuItemID generates a short random hex ID for a custom menu item.
-func generateMenuItemID() string {
+func generateMenuItemID() (string, error) {
 	b := make([]byte, 8)
-	_, _ = rand.Read(b)
-	return hex.EncodeToString(b)
+	if _, err := rand.Read(b); err != nil {
+		return "", fmt.Errorf("generate menu item ID: %w", err)
+	}
+	return hex.EncodeToString(b), nil
 }
 
 // SettingHandler 系统设置处理器
@@ -358,10 +363,18 @@ func (h *SettingHandler) UpdateSettings(c *gin.Context) {
 			}
 			// Auto-generate ID if missing
 			if strings.TrimSpace(item.ID) == "" {
-				items[i].ID = generateMenuItemID()
+				id, err := generateMenuItemID()
+				if err != nil {
+					response.Error(c, http.StatusInternalServerError, "Failed to generate menu item ID")
+					return
+				}
+				items[i].ID = id
 			} else if len(item.ID) > maxMenuItemIDLen {
 				response.BadRequest(c, "Custom menu item ID is too long (max 32 characters)")
 				return
+			} else if !menuItemIDPattern.MatchString(item.ID) {
+				response.BadRequest(c, "Custom menu item ID contains invalid characters (only a-z, A-Z, 0-9, - and _ are allowed)")
+				return
 			}
 		}
 		// ID uniqueness check

backend/internal/handler/dto/settings.go

@@ -169,3 +169,15 @@ func ParseCustomMenuItems(raw string) []CustomMenuItem {
 	}
 	return items
 }
+
+// ParseUserVisibleMenuItems parses custom menu items and filters out admin-only entries.
+func ParseUserVisibleMenuItems(raw string) []CustomMenuItem {
+	items := ParseCustomMenuItems(raw)
+	filtered := make([]CustomMenuItem, 0, len(items))
+	for _, item := range items {
+		if item.Visibility != "admin" {
+			filtered = append(filtered, item)
+		}
+	}
+	return filtered
+}

backend/internal/handler/setting_handler.go

@@ -50,7 +50,7 @@ func (h *SettingHandler) GetPublicSettings(c *gin.Context) {
 		HideCcsImportButton:         settings.HideCcsImportButton,
 		PurchaseSubscriptionEnabled: settings.PurchaseSubscriptionEnabled,
 		PurchaseSubscriptionURL:     settings.PurchaseSubscriptionURL,
-		CustomMenuItems:             dto.ParseCustomMenuItems(settings.CustomMenuItems),
+		CustomMenuItems:             dto.ParseUserVisibleMenuItems(settings.CustomMenuItems),
 		LinuxDoOAuthEnabled:         settings.LinuxDoOAuthEnabled,
 		SoraClientEnabled:           settings.SoraClientEnabled,
 		Version:                     h.version,