fix(auth): wrap JWT secret in OctKey for joserfc 1.x compatibility

joserfc 1.x requires symmetric-algorithm keys to be `OctKey` instances
rather than raw strings. Since `requirements-wheels.txt` pins
`joserfc == 1.2.*`, every call to `create_encoded_jwt()` currently raises
`joserfc.errors.MissingKeyError` at `jwt.encode`, which nginx surfaces as
`500 Internal Server Error` on `POST /api/login`. The symmetric-verify
path in `is_logged_in_without_redirect` has the same problem on
`jwt.decode`.

Reproduction

  docker exec <container> pip show joserfc    # 1.2.2
  curl -X POST -H 'Content-Type: application/json' \
       -d '{"user":"<valid-user>","password":"<valid-pw>"}' \
       http://<frigate>:5000/api/login
  # -> 500 Internal Server Error
  # log shows: joserfc.errors.MissingKeyError: missing_key

Minimal repro inside the container:

  python3 -c "
  from joserfc import jwt
  jwt.encode({'alg':'HS256'}, {'sub':'t','exp':0}, 'some-secret')
  "
  # ValueError: Invalid key

  python3 -c "
  from joserfc import jwt
  from joserfc.jwk import OctKey
  print(jwt.encode({'alg':'HS256'}, {'sub':'t','exp':0},
                   OctKey.import_key('some-secret'))[:40])
  "
  # eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiJ9...

The Home Assistant Frigate integration trips this path on every
configuration attempt because it always does `POST /api/login` with the
credentials supplied in the HA config flow, producing a confusing
"failed to connect" symptom rather than an auth error.

Fix

Wrap the secret with `OctKey.import_key(...)` at the two sites that call
into `joserfc.jwt`. The stored secret file format and everything else
stays the same; `get_jwt_secret()` continues to return a string.

AI disclosure

AI-assisted. I reviewed and tested the change end-to-end against a live
Frigate 0.17.1 container running joserfc 1.2.2: reproduced the 500 via
Home Assistant, identified the stack (auth.py line 366 in 0.17.1 / 404
on dev, and the decode call on 680), verified `OctKey.import_key(str)`
accepts the existing secret format, applied the patch in-container,
restarted, and confirmed `POST /api/login` now returns a clean
`401 {"message":"Login failed"}` for bad credentials and issues a valid
JWT cookie for good credentials. No new dependencies; `OctKey` is part
of `joserfc` which is already pinned.

frigate/api/auth.py

@@ -16,6 +16,7 @@ from typing import List, Optional
 from fastapi import APIRouter, Depends, HTTPException, Request, Response
 from fastapi.responses import JSONResponse, RedirectResponse
 from joserfc import jwt
+from joserfc.jwk import OctKey
 from peewee import DoesNotExist
 from slowapi import Limiter
 
@@ -401,10 +402,14 @@ def validate_password_strength(password: str) -> tuple[bool, Optional[str]]:
 
 
 def create_encoded_jwt(user, role, expiration, secret):
+    # joserfc 1.x requires an OctKey for symmetric algorithms instead of a
+    # raw string; passing the string raises joserfc.errors.MissingKeyError
+    # (surfaces as a 500 on POST /api/login). See requirements pin
+    # `joserfc == 1.2.*`.
     return jwt.encode(
         {"alg": "HS256"},
         {"sub": user, "role": role, "exp": expiration, "iat": int(time.time())},
-        secret,
+        OctKey.import_key(secret),
     )
 
 
@@ -677,7 +682,7 @@ def auth(request: Request):
         return fail_response
 
     try:
-        token = jwt.decode(encoded_token, request.app.jwt_token)
+        token = jwt.decode(encoded_token, OctKey.import_key(request.app.jwt_token))
         if "sub" not in token.claims:
             logger.debug("user not set in jwt token")
             return fail_response