feat(listings): add user-facing scam/abuse report flow (GOO-19)

- Add ListingFlag model with FlagReason enum (SCAM, DUPLICATE, WRONG_INFO, ALREADY_SOLD, INAPPROPRIATE)
- Add POST /listings/:id/report endpoint with rate limiting and duplicate prevention
- Auto-flag listings with ≥3 reports to PENDING_REVIEW for moderator review
- Add GET /admin/flagged-listings endpoint for admin moderation queue
- Add "Báo cáo" button + modal on listing detail page (Vietnamese UI)
- Add Prisma migration for listing_flags table with unique constraint per user/listing

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

apps/web/lib/listings-api.ts

@@ -25,6 +25,16 @@ export type Direction =
 
 export type Furnishing = 'FULLY_FURNISHED' | 'BASIC_FURNISHED' | 'UNFURNISHED';
 export type PropertyCondition = 'NEW' | 'LIKE_NEW' | 'RENOVATED' | 'USED';
+export type LegalStatus = 'SO_DO' | 'SO_HONG' | 'LAND_USE_RIGHT' | 'JOINT_USE_RIGHT' | 'AWAITING' | 'NO_CERTIFICATE';
+
+export type FlagReason = 'SCAM' | 'DUPLICATE' | 'WRONG_INFO' | 'ALREADY_SOLD' | 'INAPPROPRIATE';
+
+export interface ReportListingResult {
+  flagId: string;
+  listingId: string;
+  totalReports: number;
+  autoFlagged: boolean;
+}
 
 // ─── Interfaces ──────────────────────────────────────────
 
@@ -99,7 +109,8 @@ export interface ListingDetail {
     totalFloors: number | null;
     direction: Direction | null;
     yearBuilt: number | null;
-    legalStatus: string | null;
+    legalStatus: LegalStatus | null;
+    certificateVerified: boolean;
     amenities: string[] | null;
     nearbyPOIs: unknown;
     metroDistanceM: number | null;
@@ -303,4 +314,7 @@ export const listingsApi = {
         `/analytics/neighborhoods/${encodeURIComponent(district)}/score?city=${encodeURIComponent(city)}`,
       )
       .then((res) => res.data),
+
+  reportListing: (listingId: string, reason: FlagReason, description?: string) =>
+    apiClient.post<ReportListingResult>(`/listings/${listingId}/report`, { reason, description }),
 };