feat: websearch quota enhancements and balance notify hint

- QuotaLimit changed to *int64 (null=unlimited, >0=limited)
- Add reset-usage endpoint (POST /admin/settings/web-search-emulation/reset-usage)
- Show quota usage in header always (collapsed and expanded)
- Add reset quota button in expanded provider view
- Quota input: empty=unlimited with ∞ placeholder, must be >0 if set
- Add email verification hint on balance notify card

frontend/src/i18n/locales/en.ts

@@ -914,6 +914,7 @@ export default {
       thresholdPlaceholder: 'Enter amount',
       systemDefault: 'System Default',
       extraEmails: 'Notification Emails',
+      extraEmailsHint: 'You must add and verify an email address to receive low balance alerts',
       primaryEmail: 'Primary',
       noExtraEmails: 'No extra notification emails',
       enterEmail: 'Enter email address',
@@ -4435,10 +4436,14 @@ export default {
         copyApiKey: 'Copy',
         copied: 'Copied',
         quotaLimit: 'Quota Limit',
-        quotaLimitHint: '0 = unlimited',
+        quotaLimitHint: 'Leave empty for unlimited; must be > 0 if set',
+        quotaLimitMustBePositive: 'Quota limit must be greater than 0',
         subscribedAt: 'Subscribed At',
-        subscribedAtHint: 'Quota resets monthly from this date',
+        subscribedAtHint: 'Quota resets monthly from this date; leave empty to disable auto-reset',
         quotaUsage: 'Usage',
+        resetUsage: 'Reset',
+        resetUsageConfirm: 'Reset usage counter for this provider?',
+        resetUsageSuccess: 'Usage counter reset',
         proxy: 'Proxy',
         removeProvider: 'Remove',
         noProviders: 'No search providers configured',