feat: add admin reset subscription quota endpoint and UI

- Add AdminResetQuota service method to reset daily/weekly usage windows
- Add POST /api/v1/admin/subscriptions/:id/reset-quota handler and route
- Add resetQuota API function in frontend subscriptions client
- Add reset quota button, confirmation dialog, and handlers in SubscriptionsView
- Add i18n keys for reset quota feature in zh and en locales

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

frontend/src/i18n/locales/en.ts

@@ -1570,6 +1570,11 @@ export default {
       adjust: 'Adjust',
       adjusting: 'Adjusting...',
       revoke: 'Revoke',
+      resetQuota: 'Reset Quota',
+      resetQuotaTitle: 'Reset Usage Quota',
+      resetQuotaConfirm: "Reset the daily and weekly usage quota for '{user}'? Usage will be zeroed and windows restarted from today.",
+      quotaResetSuccess: 'Quota reset successfully',
+      failedToResetQuota: 'Failed to reset quota',
       noSubscriptionsYet: 'No subscriptions yet',
       assignFirstSubscription: 'Assign a subscription to get started.',
       subscriptionAssigned: 'Subscription assigned successfully',