openai/gpt-chat-latest → A (9:1)

Side A adds substantial user-facing and architectural functionality: persistent theme selection via cookies and a new `/theme` endpoint integrated across HTML rendering, preserves theme through authentication by reissuing cookies, and introduces room-aware URL generation (`item_path_for_api_in_room`, `forum_thread_web_url`) with broad RPC integration and tests. Side B is a valuable maintenance fix that repairs OAuth test mocks (query parsing, request-body handling, redirects, null checks, exception handling) so end-to-end auth tests work again, but its impact is confined to test infrastructure rather than core project behavior.