fix(subscriptions): atomic UsageRecord metering to prevent quota bypass

- Add @@unique([subscriptionId, metric, periodStart, periodEnd]) constraint
  to UsageRecord model with corresponding migration
- Replace racy findFirst+update/create pattern with Prisma upsert using
  INSERT ON CONFLICT DO UPDATE SET count = count + delta
- Fix CheckQuotaHandler to use period-scoped findUnique instead of
  unscoped findFirst, preventing stale cross-period reads
- Update tests to reflect atomic upsert pattern

Closes GOO-4

Co-Authored-By: Paperclip <noreply@paperclip.ing>

apps/web/app/[locale]/(public)/listings/page.tsx

@@ -19,17 +19,13 @@ import { formatPrice, formatPricePerM2 } from '@/lib/currency';
 import { useListingsSearch } from '@/lib/hooks/use-listings';
 import type { ListingDetail, PropertyType, TransactionType } from '@/lib/listings-api';
 import { PROPERTY_TYPES, TRANSACTION_TYPES } from '@/lib/validations/listings';
+import { HCM_DISTRICTS } from '@/lib/vietnam-geo';
 
 // ---------------------------------------------------------------------------
 // Hằng số
 // ---------------------------------------------------------------------------
 
-const DISTRICTS = [
-  'Quận 1', 'Quận 2', 'Quận 3', 'Quận 4', 'Quận 5', 'Quận 6', 'Quận 7',
-  'Quận 8', 'Quận 9', 'Quận 10', 'Quận 11', 'Quận 12',
-  'Bình Thạnh', 'Gò Vấp', 'Phú Nhuận', 'Tân Bình', 'Tân Phú', 'Thủ Đức',
-  'Bình Chánh', 'Hóc Môn', 'Củ Chi', 'Nhà Bè', 'Cần Giờ',
-];
+const DISTRICTS = HCM_DISTRICTS;
 
 const PRICE_RANGES = [
   { label: 'Dưới 1 tỷ', min: '', max: '1000000000' },