chore: remove unused websockets.exceptions import, add .gitignore, untrack __pycache__

- Remove unused 'import websockets.exceptions' from main.py (no reference
  to websockets.exceptions.* anywhere in the file; all WS handlers use
  broad Exception catches)
- Add .gitignore with __pycache__/, *.pyc, .venv/, and other standard
  Python excludes so bytecode no longer shows as modified in git status
- Untrack all pre-existing __pycache__/*.pyc files via git rm --cached

muxplex/main.py

@@ -24,7 +24,6 @@ from typing import Literal
 
 import httpx
 import websockets
-import websockets.exceptions
 from websockets.typing import Subprotocol
 
 from fastapi import FastAPI, Form, HTTPException, Request, WebSocket