Add post endpoint

[princechavez]

PR: Add /api/posts endpoint (initial implementation)

This PR adds a new API route at app/api/posts/route.ts to support basic post creation.
The endpoint accepts POST requests with userId, title, content, and optional labels.

Summary

• New /api/posts route handler with POST and GET methods.
• Simulates label processing by calling an external service (placeholder endpoint).
• Returns a generated ID and echoes back the post content.
• Simple logging added for debug purposes.

Testing Instructions

pnpm dev
curl -X POST http://localhost:3000/api/posts -H "content-type: application/json"   -d '{ "userId": "123", "title": "Hello", "content": "World", "labels": [{"name":"promo"}] }'