feat(listings): implement listing duplicate detection service

Add DuplicateDetector domain service that flags potential duplicate listings
using PostGIS ST_DWithin geo-proximity (100m radius) combined with trigram-based
title similarity (>70% threshold). Detection runs during CreateListing but never
blocks creation — warnings are returned in the response for seller/admin review.

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

apps/api/src/modules/listings/listings.module.ts

@@ -10,9 +10,11 @@ import { GetPendingModerationHandler } from './application/queries/get-pending-m
 import { SearchListingsHandler } from './application/queries/search-listings/search-listings.handler';
 import { LISTING_REPOSITORY } from './domain/repositories/listing.repository';
 import { PROPERTY_REPOSITORY } from './domain/repositories/property.repository';
+import { DUPLICATE_DETECTOR } from './domain/services/duplicate-detector';
 import { PrismaListingRepository } from './infrastructure/repositories/prisma-listing.repository';
 import { PrismaPropertyRepository } from './infrastructure/repositories/prisma-property.repository';
 import { MEDIA_STORAGE_SERVICE, MinioMediaStorageService } from './infrastructure/services/media-storage.service';
+import { PrismaDuplicateDetector } from './infrastructure/services/prisma-duplicate-detector';
 import { ListingsController } from './presentation/controllers/listings.controller';
 
 const CommandHandlers = [
@@ -42,6 +44,7 @@ const QueryHandlers = [
     { provide: LISTING_REPOSITORY, useClass: PrismaListingRepository },
 
     // Services
+    { provide: DUPLICATE_DETECTOR, useClass: PrismaDuplicateDetector },
     { provide: MEDIA_STORAGE_SERVICE, useClass: MinioMediaStorageService },
 
     // CQRS