feat(notify): add global toggles, percentage threshold, and visibility control

- Add global toggle for account quota notification in admin settings
- Add percentage-based threshold type for per-account quota alerts
- Hide balance notify card on user profile when global toggle is off
- Expose balance_low_notify_enabled and account_quota_notify_enabled in PublicSettings
- Add threshold type (fixed/percentage) to QuotaNotifyToggle with $ / % switcher

frontend/src/types/index.ts

@@ -117,6 +117,8 @@ export interface PublicSettings {
   oidc_oauth_provider_name: string
   backend_mode_enabled: boolean
   version: string
+  balance_low_notify_enabled: boolean
+  account_quota_notify_enabled: boolean
 }
 
 export interface AuthResponse {