Fix frequent OAuth logouts: offline_access scope, transient error handling, fetchMe resilience ...

- Add 'offline_access' to OAuth scopes so gnexus-auth issues offline
  refresh tokens instead of SSO-session-bound ones.
- Distinguish TokenRefreshException (invalid/expired refresh token)
  from transient network errors during token refresh:
  * TokenRefreshException → logout (token genuinely dead)
  * Other exceptions → fallback to cached user or API token
- Improve refresh failure logging with exc_type and error message.
- Frontend fetchMe: swallow non-401 errors so transient 5xx/network
  failures don't flash the login screen.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Add Android deep-link OAuth bridge for WebView auth ...

Problem: Android WebView opens OAuth in external browser (Chrome).
After successful login, cookie stays in Chrome and WebView remains
unauthenticated because cookies are not shared between apps.

Solution: bridge page flow that avoids cookies entirely for mobile.

Backend:
- /auth/login accepts ?platform=android and ?return_to params
- /auth/callback detects android via state metadata, skips cookie,
  redirects to /auth/mobile-done?sid=<session_id>
- /auth/mobile-done renders HTML that deep-links to navi://auth/callback

Webclient:
- login() detects NaviAndroid UA and adds ?platform=android

Android:
- MainActivity: handle incoming navi:// intent in onCreate and onNewIntent,
  set cookie via CookieManager, reload WebView
- AndroidManifest: add intent-filter for navi://auth/callback and
  singleTask launchMode

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

Dark login screen: #111 overlay, transparent card ...

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

Add full-screen login overlay for unauthenticated users ...

- Backend: new endpoint GET /auth/status returns {configured: bool}
- Webclient auth store: add authConfigured ref + fetchStatus()
- LoginScreen.vue: centered card with logo, title, and login button
- App.vue: show LoginScreen overlay when auth is configured but
  user is not authenticated (z-index 9999, blocks all UI)
- App.vue onMounted: fetch auth status before trying to resolve user

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

Multi-user auth via gnexus-auth OAuth + hybrid role/permission model ...

- Integrate gnexus-auth-client-py (GAuthClient) for OAuth flow, token refresh,
  and webhook parsing
- Add navi/auth/ package: User model, Fernet encryptor, client singleton,
  deps (get_current_user, require_admin, require_permission)
- New tables: navi_users, user_auth_sessions (auto-created on startup)
- Session/memory isolation by user_id with legacy NULL support
- Cookie-based auth proxy: /auth/login, /callback, /logout, /me
- Webhook receiver /webhooks/gnexus-auth handling user events, global logout,
  session revocation, role/permission changes
- Admin endpoints (/admin/*) gated by role + permissions
- Webclient auth store with isAdmin/hasPermission guards
- Admin-only profile filtering in /agents/profiles
- 200/200 tests passing

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