Add 404 page and invitation success screen

- Created NotFound component with proper error messaging and navigation
- Added catch-all route (*) in App.js for undefined routes
- Added success state in AcceptInvitation with user info display
- Auto-redirect after 3 seconds with manual continue button option
- Improved UX with animated success indicator

src/App.js

@@ -51,6 +51,7 @@ import ContactUs from './pages/ContactUs';
 import TermsOfService from './pages/TermsOfService';
 import PrivacyPolicy from './pages/PrivacyPolicy';
 import AcceptInvitation from './pages/AcceptInvitation';
+import NotFound from './pages/NotFound';
 
 const PrivateRoute = ({ children, adminOnly = false }) => {
   const { user, loading } = useAuth();
@@ -280,6 +281,9 @@ function App() {
               </AdminLayout>
             </PrivateRoute>
           } />
+
+          {/* 404 - Catch all undefined routes */}
+          <Route path="*" element={<NotFound />} />
         </Routes>
         <Toaster position="top-right" />
       </BrowserRouter>