openai/gpt-chat-latest → A (9:1)

Side A introduces a new structural `ItemId` type with parsing, serialization, parent/display logic, separates wire normalization into `item_wire.rs`, and migrates reducer state, ranking, routing, HTML, RPC, and tests from `CanonicalItemUrl` to the new identity model. Side B mainly improves type usage around the existing `CanonicalItemUrl` (returning it from `resolve_item`, using it consistently in collections, and adding `Deref` for URL newtypes), which is a useful cleanup but does not deliver the deeper architectural change or broad migration implemented by Side A.