feat(api): add OpenAPI/Swagger documentation for all API endpoints

Install @nestjs/swagger, configure Swagger UI at /api/docs with JWT bearer
auth, and add ApiTags/ApiOperation/ApiResponse/ApiProperty decorators to
all 8 controllers (50+ endpoints) and 31 DTOs across auth, listings,
search, payments, subscriptions, admin, notifications, and analytics modules.

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

apps/api/package.json

@@ -22,6 +22,7 @@
     "@nestjs/jwt": "^11.0.2",
     "@nestjs/passport": "^11.0.5",
     "@nestjs/platform-express": "^11.0.0",
+    "@nestjs/swagger": "^11.2.6",
     "@nestjs/throttler": "^6.5.0",
     "@paralleldrive/cuid2": "^3.3.0",
     "@prisma/client": "^6.0.0",
@@ -43,6 +44,7 @@
     "reflect-metadata": "^0.2.0",
     "rxjs": "^7.8.0",
     "sanitize-html": "^2.17.2",
+    "swagger-ui-express": "^5.0.1",
     "typesense": "^3.0.5"
   },
   "devDependencies": {