feat(listings): rate limit feature-listing via @nestjs/throttler (TEC-2930)

- Wire ThrottlerModule to a Redis-backed storage (shared across API
  instances) using @nest-lab/throttler-storage-redis.
- Add FeatureListingThrottlerGuard that tracks per-user when JWT is
  present, falling back to the real client IP behind the reverse proxy —
  keeps per-user and per-IP buckets independent.
- Apply @Throttle({ default: { limit: 10, ttl: 60_000 } }) + the guard
  to POST /listings/:id/feature and document 429 in Swagger.
- Integration test (feature-listing-throttle.integration.spec.ts)
  verifies: 10 reqs pass / 11th returns 429 with Retry-After, separate
  IPs keep their own quotas, and the tracker key logic.

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

apps/api/package.json

@@ -17,6 +17,7 @@
     "@aws-sdk/client-s3": "^3.1026.0",
     "@aws-sdk/s3-request-presigner": "^3.1026.0",
     "@goodgo/mcp-servers": "workspace:*",
+    "@nest-lab/throttler-storage-redis": "^1.2.0",
     "@nestjs/bullmq": "^11.0.4",
     "@nestjs/common": "^11.0.0",
     "@nestjs/config": "^4.0.4",