Backend:
- User model: add avatar_url field
- auth/deps.py: extract avatar_url from auth_user.profile (picture/avatar_url)
- auth.py /auth/me: return avatar_url + computed profile_url
- config.py: add gnauth_profile_path setting
- .env.example: document GNAUTH_PROFILE_PATH

Frontend:
- AppSidebar.vue: show user avatar (or initial fallback) next to name
- Clicking user info opens gnexus-auth profile in new tab
- Rebuild dist/

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>