Add /manage/profile page where authenticated users can view and edit
their OIDC profile fields (given_name, family_name, preferred_username,
email, phone_number, picture, locale).
- Create manage/base.html with tab-style nav for Profile/Credentials
- Update credentials.html to extend manage/base.html
- Add GET/POST routes with server-side validation
- Add input styling for tel and url input types
- Add profile test user with pre-filled data in setup_db.py
- Add 19 E2E tests covering structure, navigation, updates, validation
- All 76 E2E tests and 172 Python tests pass
