feat(auth): admin OIDC settings page

New admin page /settings/oidc to configure the OIDC provider (issuer,
client id/secret, redirect/callback URL, scopes, post-login redirect).
Prominently shows the callback URL to register at the IdP, current
status/source, and the read-only deploy-level OIDC-only flag. Secret
is write-only (blank = keep). Sidebar entry for admins.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/App.tsx

@@ -21,6 +21,7 @@ import CalendarPage from '@/pages/CalendarPage'
 import SupportDetailPage from '@/pages/SupportDetailPage'
 import MeetingDetailPage from '@/pages/MeetingDetailPage'
 import OidcCallbackPage from '@/pages/OidcCallbackPage'
+import OidcSettingsPage from '@/pages/OidcSettingsPage'
 import axios from 'axios'
 
 const getStoredWizardPort = (): number | null => {
@@ -135,6 +136,7 @@ export default function App() {
             <Route path="/roles" element={<RoleEditorPage />} />
             <Route path="/users" element={<UsersPage />} />
             <Route path="/monitor" element={<MonitorPage />} />
+            <Route path="/settings/oidc" element={<OidcSettingsPage />} />
             <Route path="/oidc/callback" element={<OidcCallbackPage onToken={loginWithToken} />} />
             <Route path="*" element={<Navigate to="/" />} />
           </Routes>