openai/gpt-chat-latest → A (4:1)

Side A makes a substantive architectural improvement by introducing a settlement worker that batches vote persistence and ranking recomputation, adds cached ranking reads (`ranked_items_cached`) to avoid unnecessary recomputation and write locks on HTTP requests, and removes the temporary demo-counter feature and its related event/UI code. Side B is largely a UI and routing enhancement for persistent themes plus correct room-specific URL generation in RPC responses, which is useful but less foundational than the concurrency, caching, and cleanup changes in Side A.