fix: abort old loads, stale sync state, warn before unsaved edits are lost

src/App.jsx

@@ -25,6 +25,7 @@ import PageBackground from './components/PageBackground.jsx';
 import {usePreferences} from './context/PreferencesContext.jsx';
 import {clearSession} from './utils/auth.js';
 import useSession from './hooks/useSession.js';
+import {UnsavedChangesGuard} from './hooks/useUnsavedChanges.js';
 import {logout} from './utils/api.js';
 
 function App() {
@@ -84,6 +85,7 @@ function App() {
                     </Link>
                 </footer>
             </div>
+            <UnsavedChangesGuard/>
             <Toaster richColors position="bottom-right"/>
         </TooltipProvider>
     );