Integrate Vue webclient into server: serve SPA from /, remove proxy.php, update auth redirects

Route all auth/login requests through proxy.php for cross-domain SPA ...

- Replace direct /auth/login with /proxy.php?path=/auth/login so the
  request reaches the PHP backend through proxy.php when the SPA runs
  on a different domain (panel.smarthome.arp vs 192.168.1.101).
- Pass full window.location.href as return_to so the OAuth callback
  redirects back to the panel domain, not the bare server IP.

Fix logout: session_start + destroy cookie + redirect to local /login instead of /auth/login

Phase 4: Vue client auth store, Bearer token injection, router guards, login page ...

Server:
- AuthControllerTrait now supports both session and Bearer token auth
  (resolves user from Authorization: Bearer header via shserv_sessions)

Vue client:
- Add api/auth.js module for access token management
- Inject Authorization: Bearer header in http.js
- Handle 401 in client.js: clear token + redirect to /auth/login
- New Pinia auth store (stores/auth.js): init, refreshToken, logout, hasPermission
- New usePermission composable
- Router guards: redirect unauthenticated to /login, permission-based route blocking
- New LoginPage.vue with gnexus-auth login button
- AppShell: conditional nav items by permission, user bar with logout
- main.js: initialize auth before mounting app
- MSW mocks: /auth/me, /auth/logout, /auth/refresh
- Fix AppShell.spec.js for Pinia + router setup

All 167 tests pass.