Add persistent Undo button to TopBar

src/App.tsx

@@ -305,6 +305,9 @@ export default function App() {
         hasUnsavedChanges={appState.hasUnsavedChanges}
         userEmail={session.user.email}
         onSignOut={handleSignOut}
+        canUndo={!!undoState}
+        onUndo={handleUndo}
+        undoMessage={undoState?.message}
       />
       <div className="flex flex-1 overflow-hidden">
         <Sidebar activeModule={activeModule} setActiveModule={setActiveModule} />