Create core backend skeleton #6

Goal: Initialize the new core-backend service using FastAPI to act as the primary API Gateway and business logic handler.
Tasks:

Initialize a new Poetry project in apps/core-backend.

Install core dependencies: fastapi, uvicorn, pydantic.

Set up the 3-tier folder structure (api/routers, services, repositories).

Create a basic main.py entry point with a /health check endpoint.

Ensure the service runs locally on port 8000.