home: Show unread count on Channels button in main menu

Add a counter badge showing the number of unread channel messages
on the Channels button in the main menu. The count is computed as
countInCombinedFeedNarrow() - countInDms(), matching the web app.

Also add an explicit test confirming that _CombinedFeedButton does
not show a counter badge, documenting the intentional absence.

Fixes-partly: zulip#1088

Author: Khader-1

lib/widgets/home.dart

@@ -755,6 +755,21 @@ class _ChannelsButton extends _NavigationBarMenuButton {
     return zulipLocalizations.channelsPageTitle;
   }
 
+  @override
+  Widget? buildTrailing(BuildContext context) {
+    final store = PerAccountStoreWidget.of(context);
+    final unreads = store.unreads;
+    final unreadCount =
+      unreads.countInCombinedFeedNarrow() - unreads.countInDms();
+    if (unreadCount == 0) return null;
+    return CounterBadge(
+      kind: CounterBadgeKind.unread,
+      style: CounterBadgeStyle.mainMenu,
+      count: unreadCount,
+      channelIdForBackground: null,
+    );
+  }
+
   @override
   _HomePageTab get navigationTarget => _HomePageTab.channels;
 }

test/widgets/home_test.dart

@@ -495,6 +495,52 @@ void main () {
       });
     });
 
+    group('_ChannelsButton counter', () {
+      final findButton = find.byWidgetPredicate((widget) =>
+        widget is MenuButton && widget.icon == ZulipIcons.hash_italic);
+
+      testWidgets('no badge when no unread channel messages', (tester) async {
+        await prepare(tester);
+        await tapOpenMenuAndAwait(tester);
+        check(find.descendant(
+          of: findButton, matching: find.byType(CounterBadge))).findsNothing();
+        debugNetworkImageHttpClientProvider = null;
+      });
+
+      testWidgets('shows unread channel message count', (tester) async {
+        await prepare(tester);
+        await addUnreadStreamMessage();
+        await tapOpenMenuAndAwait(tester);
+        check(find.descendant(
+          of: findButton, matching: find.text('1'))).findsOne();
+        debugNetworkImageHttpClientProvider = null;
+      });
+
+      testWidgets('does not count DM unreads', (tester) async {
+        await prepare(tester);
+        final dmMessage = eg.dmMessage(from: eg.otherUser, to: [eg.selfUser]);
+        await store.addMessage(dmMessage);
+        await tapOpenMenuAndAwait(tester);
+        check(find.descendant(
+          of: findButton, matching: find.byType(CounterBadge))).findsNothing();
+        debugNetworkImageHttpClientProvider = null;
+      });
+    });
+
+    group('_CombinedFeedButton', () {
+      final findButton = find.byWidgetPredicate((widget) =>
+        widget is MenuButton && widget.icon == ZulipIcons.message_feed);
+
+      testWidgets('no counter badge', (tester) async {
+        await prepare(tester);
+        await addUnreadStreamMessage();
+        await tapOpenMenuAndAwait(tester);
+        check(find.descendant(
+          of: findButton, matching: find.byType(CounterBadge))).findsNothing();
+        debugNetworkImageHttpClientProvider = null;
+      });
+    });
+
     group('_DirectMessagesButton counter', () {
       final findButton = find.byWidgetPredicate((widget) =>
         widget is MenuButton && widget.icon == ZulipIcons.two_person);