chore: drop python-jose, nothing imports it (#27444)

The migration to joserfc completed the job but left the old dependency pinned. `python-jose` now has zero imports anywhere in the backend: the only `jose` references left are `joserfc` in `utils/oauth.py`, and a repo-wide search for `from jose`, `import jose` or `python_jose` returns nothing outside the three pin files.

Removing it also removes `ecdsa` and `rsa` from the image, which were pulled in only by python-jose. `uv lock` confirms that: it drops exactly those three packages and nothing else, because google-auth 2.55 depends on cryptography and pyasn1-modules rather than rsa. That is worth having beyond the size saving, since `ecdsa` ships a documented Minerva-style timing side-channel in its P-256 signing path that upstream has declined to fix, so keeping it in the image means shipping a flagged crypto library that nothing calls.

Verified by blocking the `jose` module at import time and importing the backend anyway:

```
PASS  import open_webui.utils.auth
PASS  import open_webui.utils.oauth
PASS  import open_webui.main
jose in sys.modules: False
PASS  create_token/decode_token round trip
```

One user-visible consequence worth stating: Tools and Functions run in the same interpreter, so a third-party plugin that imports `jose` directly stops working after this. Nothing in Open WebUI itself does, and PyJWT remains a dependency, but a plugin relying on a library the application never declared for that purpose is the only thing this can break.

`uv.lock` was edited surgically rather than regenerated, to avoid the unrelated whole-file churn a newer uv version introduces. The result was diffed against real `uv lock` output and matches it exactly apart from that version's cosmetic fields.

backend/requirements-min.txt

@@ -8,7 +8,6 @@ python-multipart==0.0.32
 itsdangerous==2.2.0
 
 python-socketio==5.16.2
-python-jose==3.5.0
 cryptography
 bcrypt==5.0.0
 argon2-cffi==25.1.0

backend/requirements.txt

@@ -5,7 +5,6 @@ python-multipart==0.0.32
 itsdangerous==2.2.0
 
 python-socketio==5.16.2
-python-jose==3.5.0
 cryptography==48.0.0
 bcrypt==5.0.0
 argon2-cffi==25.1.0