openai/gpt-chat-latest → A (4:1)

Side A adds substantial new infrastructure: a new `/ui` endpoint with `HtmlUiAction` parsing, JSON form-template substitution (`form_template.rs`), reusable web-post handlers, and UI expansion flows for thread forms, introducing a reusable browser UI command architecture. Side B is largely a refactor that centralizes room URL encoding/decoding (`room_route_segment`/`room_id_from_route_segment`) and updates routes plus some URL normalization utilities, which improves consistency but is narrower in scope and mostly restructures existing behavior.