FIX: bookmark control should track a topic model change (#35867)

This change fixes the issue with a leaking bookmark state when
transitioning between different topics.

frontend/discourse/app/components/bookmark-menu.gjs

@@ -23,7 +23,6 @@ export default class BookmarkMenu extends Component {
   @tracked quicksaved = false;
   @tracked reminderAtOptions = [];
 
-  bookmarkManager = this.args.bookmarkManager;
   timezone = this.currentUser?.user_option?.timezone || moment.tz.guess();
   timeShortcuts = timeShortcuts(this.timezone);
   bookmarkCreatePromise = null;
@@ -41,6 +40,10 @@ export default class BookmarkMenu extends Component {
     this.reminderAtOptions.push(custom);
   }
 
+  get bookmarkManager() {
+    return this.args.bookmarkManager;
+  }
+
   get existingBookmark() {
     return this.bookmarkManager.trackedBookmark?.id
       ? this.bookmarkManager.trackedBookmark

spec/system/bookmarks_spec.rb

@@ -2,9 +2,11 @@
 
 describe "Bookmarking posts and topics", type: :system do
   fab!(:topic)
+  fab!(:topic_2, :topic)
   fab!(:current_user) { Fabricate(:user, refresh_auto_groups: true) }
   fab!(:post) { Fabricate(:post, topic: topic, raw: "This is some post to bookmark") }
   fab!(:post_2) { Fabricate(:post, topic: topic, raw: "Some interesting post content") }
+  fab!(:post_3) { Fabricate(:post, topic: topic_2, raw: "Check out this [topic](/t/#{topic.id})") }
 
   let(:timezone) { "Australia/Brisbane" }
   let(:cdp) { PageObjects::CDP.new }
@@ -116,6 +118,16 @@ describe "Bookmarking posts and topics", type: :system do
         bookmark.reminder_at_in_zone(timezone).strftime("%H:%M"),
       )
     end
+
+    it "bookmark button is topic specific" do
+      topic_page.visit_topic(topic_2)
+      topic_page.click_topic_bookmark_button
+      expect(topic_page).to have_topic_bookmarked(topic_2)
+
+      # transition to another topic w/o refreshing the page
+      find("a[href='/t/#{topic.id}']").click
+      expect(topic_page).to have_no_bookmarks(topic)
+    end
   end
 
   describe "editing existing bookmarks" do