fix: resolve flaky chats system test race condition (#1375)

Wait for the chat to fully load after click before triggering a page
refresh, ensuring last_viewed_chat is persisted server-side.

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

test/system/chats_test.rb

@@ -32,17 +32,23 @@ class ChatsTest < ApplicationSystemTestCase
   test "sidebar shows last viewed chat" do
     with_env_overrides OPENAI_ACCESS_TOKEN: "test-token" do
       @user.update!(ai_enabled: true)
+      chat_title = @user.chats.first.title
 
       visit root_url
 
-      click_on @user.chats.first.title
+      click_on chat_title
+
+      # Wait for the chat to actually load before refreshing
+      within "#chat-container" do
+        assert_selector "h1", text: chat_title
+      end
 
       # Page refresh
       visit root_url
 
       # After page refresh, we're still on the last chat we were viewing
       within "#chat-container" do
-        assert_selector "h1", text: @user.chats.first.title
+        assert_selector "h1", text: chat_title
       end
     end
   end