feat(api-key): add independent quota and expiration support

This feature allows API Keys to have their own quota limits and expiration
times, independent of the user's balance.

Backend:
- Add quota, quota_used, expires_at fields to api_key schema
- Implement IsExpired() and IsQuotaExhausted() checks in middleware
- Add ResetQuota and ClearExpiration API endpoints
- Integrate quota billing in gateway handlers (OpenAI, Anthropic, Gemini)
- Include quota/expiration fields in auth cache for performance
- Expiration check returns 403, quota exhausted returns 429

Frontend:
- Add quota and expiration inputs to key create/edit dialog
- Add quick-select buttons for expiration (+7, +30, +90 days)
- Add reset quota confirmation dialog
- Add expires_at column to keys list
- Add i18n translations for new features (en/zh)

Migration:
- Add 045_add_api_key_quota.sql for new columns

frontend/src/i18n/locales/en.ts

@@ -407,6 +407,7 @@ export default {
     usage: 'Usage',
     today: 'Today',
     total: 'Total',
+    quota: 'Quota',
     useKey: 'Use Key',
     useKeyModal: {
       title: 'Use API Key',
@@ -470,6 +471,33 @@ export default {
       geminiCli: 'Gemini CLI',
       geminiCliDesc: 'Import as Gemini CLI configuration',
     },
+    // Quota and expiration
+    quotaLimit: 'Quota Limit',
+    quotaAmount: 'Quota Amount (USD)',
+    quotaAmountPlaceholder: 'Enter quota limit in USD',
+    quotaAmountHint: 'Set the maximum amount this key can spend. 0 = unlimited.',
+    quotaUsed: 'Quota Used',
+    reset: 'Reset',
+    resetQuotaUsed: 'Reset used quota to 0',
+    resetQuotaTitle: 'Confirm Reset Quota',
+    resetQuotaConfirmMessage: 'Are you sure you want to reset the used quota (${used}) for key "{name}" to 0? This action cannot be undone.',
+    quotaResetSuccess: 'Quota reset successfully',
+    failedToResetQuota: 'Failed to reset quota',
+    expiration: 'Expiration',
+    expiresInDays: '{days} days',
+    extendDays: '+{days} days',
+    customDate: 'Custom',
+    expirationDate: 'Expiration Date',
+    expirationDateHint: 'Select when this API key should expire.',
+    currentExpiration: 'Current expiration',
+    expiresAt: 'Expires',
+    noExpiration: 'Never',
+    status: {
+      active: 'Active',
+      inactive: 'Inactive',
+      quota_exhausted: 'Quota Exhausted',
+      expired: 'Expired',
+    },
   },
 
   // Usage