- Add UserSession and QRLoginChallenge models for session tracking
and mobile QR authentication
- Add session_manager utility with create/validate/revoke/cleanup
functions and QR challenge helpers
- Add /api/sessions endpoints for listing, revoking, and
'log off everywhere' functionality
- Add /api/qr-auth endpoints for challenge creation, polling, and
claiming with API token issuance
- Add session config fields (lifetime, custom override, QR TTL)
- Update get_current_user to validate server-side sessions
- Create server-side sessions on all login paths (local, OAuth,
social, admin)
- Revoke server-side session on logout
- Configure SessionMiddleware max_age from session lifetime settings
- Graceful degradation: old sessions without _session_token continue
to work
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>