feat: implement OAuth 2.0 / OpenID Connect support

- Added OAuth configuration management in the admin panel.
- Implemented OAuth authorization flow with PKCE for enhanced security.
- Created routes for handling OAuth provider discovery, authorization, and callback.
- Integrated OAuth login and registration options in the frontend.
- Updated UI components to support OAuth login and registration.
- Added internationalization strings for OAuth-related messages.
- Implemented encryption for client secrets and secure state management.
- Added error handling and user feedback for OAuth processes.

src/App.jsx

@@ -17,6 +17,7 @@ import GuestJoin from './pages/GuestJoin';
 import FederationInbox from './pages/FederationInbox';
 import FederatedRoomDetail from './pages/FederatedRoomDetail';
 import Calendar from './pages/Calendar';
+import OAuthCallback from './pages/OAuthCallback';
 
 export default function App() {
   const { user, loading } = useAuth();
@@ -50,6 +51,7 @@ export default function App() {
       <Route path="/login" element={user ? <Navigate to="/dashboard" /> : <Login />} />
       <Route path="/register" element={user ? <Navigate to="/dashboard" /> : <Register />} />
       <Route path="/verify-email" element={<VerifyEmail />} />
+      <Route path="/oauth/callback" element={<OAuthCallback />} />
       <Route path="/join/:uid" element={<GuestJoin />} />
 
       {/* Protected routes */}