Add FastAPI real-time chat template

[sureshchouksey8]

Fixes #3.

Adds a Codesphere-ready FastAPI real-time chat application template. This is a full single-workspace example with WebSockets, demo authentication, SQLite message history, static frontend assets, tests, and CI.

Included:

• FastAPI app under fastapi-realtime-chat/
• demo token-based login for ada, grace, and linus
• websocket room broadcasting for general, product, and support
• SQLite persistence with initialization script
• browser UI with room switching and live messages
• Codesphere ci.yml for install, DB init, tests, and run
• README with local setup, Codesphere usage, and article draft

Validation:

• python3 -m venv .venv
• pip install -r requirements.txt
• python scripts/init_db.py
• pytest
• local uvicorn app.main:app run
• Chromium/Playwright smoke test: sign in, open #general, send and receive a websocket message