openai/gpt-chat-latest → A (4:1)

Side A substantially refactors the test infrastructure by extracting duplicated HTTP/OAuth helpers, test assertions, server environment construction, and cargo build logic into shared modules (`test.common` and `test.oauth`), then updates multiple integration test suites to use them. It also adds reusable capabilities such as configurable mock Google users, registration helpers, and standardized HTTP timeouts, reducing duplication and making future test maintenance easier, whereas Side B mainly simplifies one UI flow by removing the `ExpandNewThreadForm` action and server-rendering the existing compose slot on the home page.