openai/gpt-chat-latest → A (9:2)

Side A performs a foundational identity refactor by introducing a structural `ItemId` type, extracting normalization into `item_wire`, and propagating the new type through the reducer, ranking, routing, RPC, HTML, and tests. Side B adds useful theme persistence and room-aware URL generation, but its changes are primarily UI and presentation plumbing, whereas Side A changes the project's core data model and eliminates widespread dependence on `CanonicalItemUrl` strings.