optimized avatar and linkify performance, refined navigation to preserve popups, implemented read marker caching, and added file size limits for saving, minor timetable details changes

lib/app.dart

@@ -38,6 +38,9 @@ class App extends StatefulWidget {
 class _AppState extends State<App> with WidgetsBindingObserver {
   late Timer _updateTimings;
   StreamSubscription<dynamic>? _timetableWidgetSync;
+  StreamSubscription<RemoteMessage>? _onMessageSub;
+  StreamSubscription<RemoteMessage>? _onMessageOpenedAppSub;
+  StreamSubscription<String>? _fcmTokenRefreshSub;
   // Tracked via the bottom-nav controller's listener so it always reflects the
   // user's actual position, even between rapid setting emits where the
   // controller hasn't caught up to a scheduled jump yet.
@@ -84,10 +87,12 @@ class _AppState extends State<App> with WidgetsBindingObserver {
     // Routes pushed with `withNavBar: false` (chat views, file viewers, …)
     // sit on the root navigator above the bottom-nav, so a bare jumpToTab
     // would swap the tab behind them and leave the user staring at the
-    // previous screen. Reset to the tab root first.
+    // previous screen. Reset to the tab root first — but stop at any open
+    // popup so a confirmation dialog or bottom sheet that the user hasn't
+    // dismissed yet doesn't get silently torn down.
     final navigator = Navigator.of(context);
     if (navigator.canPop()) {
-      navigator.popUntil((route) => route.isFirst);
+      navigator.popUntil((route) => route.isFirst || route is PopupRoute);
     }
     AppRoutes.goToTab(context, Modules.timetable);
   }
@@ -98,10 +103,11 @@ class _AppState extends State<App> with WidgetsBindingObserver {
     if (share == null) return;
     // A second share arriving while a previous share-flow page is still on
     // the stack would otherwise leave the old page sitting on top with stale
-    // (already-cleared) file paths. Reset to the tab root before pushing.
+    // (already-cleared) file paths. Reset to the tab root before pushing —
+    // but stop at any open popup so dialogs/bottom-sheets remain intact.
     final navigator = Navigator.of(context);
     if (navigator.canPop()) {
-      navigator.popUntil((route) => route.isFirst);
+      navigator.popUntil((route) => route.isFirst || route is PopupRoute);
     }
     AppRoutes.openShareTarget(context, share);
   }
@@ -165,11 +171,13 @@ class _AppState extends State<App> with WidgetsBindingObserver {
 
     if (context.read<SettingsCubit>().val().notificationSettings.enabled) {
       void update() => NotifyUpdater.registerToServer();
-      FirebaseMessaging.instance.onTokenRefresh.listen((_) => update());
+      _fcmTokenRefreshSub = FirebaseMessaging.instance.onTokenRefresh.listen(
+        (_) => update(),
+      );
       update();
     }
 
-    FirebaseMessaging.onMessage.listen((message) {
+    _onMessageSub = FirebaseMessaging.onMessage.listen((message) {
       if (!mounted) return;
       NotificationController.onForegroundMessageHandler(message, context);
     });
@@ -177,7 +185,9 @@ class _AppState extends State<App> with WidgetsBindingObserver {
       NotificationController.onBackgroundMessageHandler,
     );
 
-    FirebaseMessaging.onMessageOpenedApp.listen((message) {
+    _onMessageOpenedAppSub = FirebaseMessaging.onMessageOpenedApp.listen((
+      message,
+    ) {
       if (!mounted) return;
       NotificationController.onAppOpenedByNotification(message, context);
     });
@@ -193,6 +203,9 @@ class _AppState extends State<App> with WidgetsBindingObserver {
   void dispose() {
     _updateTimings.cancel();
     _timetableWidgetSync?.cancel();
+    _onMessageSub?.cancel();
+    _onMessageOpenedAppSub?.cancel();
+    _fcmTokenRefreshSub?.cancel();
     ShareIntentListener.pending.removeListener(_handlePendingShare);
     ShareIntentListener.instance.detach();
     Main.bottomNavigator.removeListener(_onTabControllerChanged);
@@ -279,7 +292,12 @@ class _AppState extends State<App> with WidgetsBindingObserver {
           key: ValueKey(config.items.length),
           navBarConfig: config,
           navBarDecoration: NavBarDecoration(
-            border: const Border(top: BorderSide(width: 1, color: Colors.grey)),
+            border: Border(
+              top: BorderSide(
+                width: 1,
+                color: Theme.of(context).colorScheme.outlineVariant,
+              ),
+            ),
             color: Theme.of(context).colorScheme.surface,
           ),
         ),