~anthropic/claude-sonnet-latest → B (65:35)

Commit B is a substantial, functionally significant change: it moves theme selection from client-only JS/localStorage to a server-rendered, cookie-based, SSR-consistent mechanism (new /theme route, cookie helpers, layout signature changes across every page handler) and also adds room-aware URL rewriting for API/RPC responses (item_path_for_api_in_room, forum_thread_web_url) with accompanying tests, fixing real correctness gaps for private rooms. Commit A is a smaller, well-tested fix improving color gradient semantics for rank rows, which is valuable but narrower in scope and impact than B's cross-cutting architectural and correctness improvements.