feat: Add user notification settings with quota warning and multiple notification methods

- Implement user notification settings with email and webhook options
- Add new user settings for quota warning threshold and notification preferences
- Create backend API and database support for user notification configuration
- Enhance frontend personal settings with notification configuration UI
- Support custom notification email and webhook URL
- Add service layer for sending user notifications

web/src/helpers/render.js

@@ -386,7 +386,7 @@ export function renderQuotaWithPrompt(quota, digits) {
   let displayInCurrency = localStorage.getItem('display_in_currency');
   displayInCurrency = displayInCurrency === 'true';
   if (displayInCurrency) {
-    return '|' + i18next.t('等价金额') + ': ' + renderQuota(quota, digits) + '';
+    return ' | ' + i18next.t('等价金额') + ': ' + renderQuota(quota, digits) + '';
   }
   return '';
 }