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/stores/app.ts

@@ -339,7 +339,9 @@ export const useAppStore = defineStore('app', () => {
         oidc_oauth_enabled: false,
         oidc_oauth_provider_name: 'OIDC',
         backend_mode_enabled: false,
-        version: siteVersion.value
+        version: siteVersion.value,
+        balance_low_notify_enabled: false,
+        account_quota_notify_enabled: false,
       }
     }