FIX: update bookmark UI when using keyboard shortcut (#37639)

When pressing B then Enter to bookmark a topic, the bookmark icon next
to the topic title and the topic footer bookmark button did not update
until page reload.

The keyboard shortcut path opens the BookmarkModal directly via the
topic controller, bypassing the TopicBookmarkManager that the footer's
BookmarkMenu component relies on. The afterSave callback correctly sets
`topic.bookmarked = true`, but the `topicBookmarkManager` computed
property only depended on `"topic"` (the object identity), so it never
recreated the manager to pick up the new bookmark state.

Changed the dependent key to `"topic.bookmarked"` so the manager is
recreated whenever the bookmarked property changes, regardless of which
code path triggered it.

frontend/discourse/app/components/topic-footer-buttons.gjs

@@ -66,7 +66,7 @@ export default class TopicFooterButtons extends Component {
     );
   }
 
-  @computed("topic")
+  @computed("topic.bookmarked")
   get topicBookmarkManager() {
     return new TopicBookmarkManager(getOwner(this), this.topic);
   }

spec/system/bookmarks_spec.rb

@@ -119,6 +119,21 @@ describe "Bookmarking posts and topics", type: :system do
       )
     end
 
+    it "updates the topic status and footer button when using the keyboard shortcut" do
+      topic_page.visit_topic(topic)
+      expect(topic_page).to have_no_topic_status_bookmark
+      expect(topic_page).to have_no_bookmarks(topic)
+
+      send_keys("b")
+      expect(bookmark_modal).to be_open
+      send_keys(:enter)
+      expect(bookmark_modal).to be_closed
+
+      expect(topic_page).to have_topic_status_bookmark
+      expect(topic_page).to have_topic_bookmarked(topic)
+      expect(Bookmark.exists?(bookmarkable: topic, user: current_user)).to eq(true)
+    end
+
     it "bookmark button is topic specific" do
       topic_page.visit_topic(topic_2)
       topic_page.click_topic_bookmark_button

spec/system/page_objects/pages/topic.rb

@@ -224,6 +224,14 @@ module PageObjects
         within_topic_footer_buttons { has_no_css?(".bookmark-menu-trigger.bookmarked") }
       end
 
+      def has_topic_status_bookmark?
+        has_css?("#topic-title .topic-status.--bookmarked")
+      end
+
+      def has_no_topic_status_bookmark?
+        has_no_css?("#topic-title .topic-status.--bookmarked")
+      end
+
       def click_reply_button
         within_topic_footer_buttons { find(".create").click }
         has_expanded_composer?