openai/gpt-chat-latest → A (3:2)

Side A simplifies the UI architecture by removing the `ExpandNewThreadForm` action and its server-side dispatch logic, and instead server-renders the collapsed compose/login state directly into `#new-thread-ui-slot` on the home page, eliminating duplicated flows and obsolete parsing/tests. Side B improves sibling navigation by placing each unranked sibling into its own group and adds a regression test, but it is a narrower behavioral adjustment compared with A's broader reduction of redundant code paths.