openai/gpt-5.2-chat → B (9:1)

Side A is purely a formatting commit (import reordering, line wrapping, no behavioral changes). Side B introduces substantive functionality: a full theme system with cookie handling (`post_theme`, `theme_from_jar`, layout changes), propagates theme through auth/editor/forum/garden/search pages, and adds room-aware URL helpers (`item_path_for_api_in_room`, `forum_thread_web_url`) with extensive RPC integration and tests—clearly adding lasting user-facing and API value.