Implement code word based remote authentication (#1)

Add comprehensive remote authentication system allowing users to log in from one device by authenticating from another trusted device. Features include:

- Proof of Work (PoW) protection using PBKDF2-SHA512 to prevent abuse
- Simple pairing codes (3 words) protected by dynamic PoW difficulty
- Autocomplete pairing code input with error checking
- Real-time WebSocket communication between devices

Unlike device addition links and reset links with QR codes that only allow adding an authentication method, and that work offline over the duration of several days, this mechanism is strictly online, with 5 minute time limit.

paskia/fastapi/auth_host.py

@@ -73,7 +73,7 @@ def redirect_to_root_on_auth_host(request: Request, cur: str, path: str) -> Resp
 
 async def redirect_middleware(request: Request, call_next):
     """Middleware to handle auth host redirects."""
-    cfg = hostutil.configured_auth_host()
+    cfg = hostutil.dedicated_auth_host()
     if not cfg:
         return await call_next(request)