add threads button back to appbar, hide close button on linux mobile mode

lib/widgets/appbar.dart

@@ -77,6 +77,12 @@ final class const Appbar({
                 onPressed: maximize,
                 icon: const Icon(Icons.fullscreen),
               ),
+            if (ref
+                    .watch(SettingsController.provider)
+                    .whenOrNull(
+                      data: (settings) => !settings.linuxMobileMode,
+                    ) ??
+                true)
               IconButton(
                 tooltip: "Close window",
                 onPressed: () => exit(0),

lib/widgets/room_appbar.dart

@@ -63,6 +63,11 @@ final class const RoomAppbar({
         room == null
             ? []
             : [
+                IconButton(
+                  onPressed: onOpenThreads?.call,
+                  icon: Icon(Icons.forum),
+                  tooltip: "Open threads",
+                ),
                 IconButton(
                   onPressed: onOpenPinnedMessagesList?.call,
                   icon: Icon(Icons.push_pin),
@@ -73,11 +78,7 @@ final class const RoomAppbar({
                   tooltip: "Open member list",
                   icon: Icon(Icons.people),
                 ),
-                RoomMenuButton(
-                  room,
-                  onOpenSearch: onOpenSearch,
-                  onOpenThreads: onOpenThreads,
-                ),
+                RoomMenuButton(room, onOpenSearch: onOpenSearch),
               ],
       ),
     );

lib/widgets/room_menu_button.dart

@@ -17,7 +17,6 @@ final class const RoomMenuButton(
   final Room? room, {
   final IList<Room> children = const .empty(),
   final VoidCallback? onOpenSearch,
-  final VoidCallback? onOpenThreads,
   super.key,
 }) extends ConsumerWidget {
   @override
@@ -29,19 +28,11 @@ final class const RoomMenuButton(
       icon: const Icon(Icons.more_vert),
       tooltip: "Room options",
       itemBuilder: (_) => [
-        if (onOpenSearch case final onOpenSearch?)
+        if (onOpenSearch != null)
           PopupMenuItem(
             onTap: onOpenSearch,
             child: ListTile(leading: Icon(Icons.search), title: Text("Search")),
           ),
-        if (onOpenThreads case final onOpenThreads?)
-          PopupMenuItem(
-            onTap: onOpenThreads,
-            child: ListTile(
-              leading: Icon(Icons.forum),
-              title: Text("View Threads"),
-            ),
-          ),
         PopupMenuItem(
           onTap: () async {
             if (room != null) await client.markRead(room!);