FIX: Chat threads N1 (#22322)

Followup to 1526d1f97d4617b5de03db8b71cd02cb1802d49c

This commit fixes an N1 for mentions/user status
when querying chat threads. This only happened if
any of the thread OMs had mentions.

plugins/chat/spec/requests/chat/api/channel_threads_controller_spec.rb

@@ -124,6 +124,38 @@ RSpec.describe Chat::Api::ChannelThreadsController do
       )
     end
 
+    it "has preloaded chat mentions and users for the thread original message" do
+      thread_1.original_message.update!(
+        message: "@#{current_user.username} hello and @#{thread_2.original_message_user.username}!",
+      )
+      thread_1.original_message.rebake!
+      thread_1.original_message.create_mentions
+
+      get "/chat/api/channels/#{public_channel.id}/threads"
+      expect(response.status).to eq(200)
+      expect(
+        response.parsed_body["threads"]
+          .find { |thread| thread["id"] == thread_1.id }
+          .dig("original_message", "mentioned_users"),
+      ).to eq(
+        [
+          {
+            "avatar_template" => User.system_avatar_template(current_user.username),
+            "id" => current_user.id,
+            "name" => current_user.name,
+            "username" => current_user.username,
+          },
+          {
+            "avatar_template" =>
+              User.system_avatar_template(thread_2.original_message_user.username),
+            "id" => thread_2.original_message_user.id,
+            "name" => thread_2.original_message_user.name,
+            "username" => thread_2.original_message_user.username,
+          },
+        ],
+      )
+    end
+
     context "when the channel is not accessible to the useer" do
       before do
         public_channel.update!(chatable: Fabricate(:private_category, group: Fabricate(:group)))