openai/gpt-chat-latest → A (3:2)

Side A introduces a new `ItemId` type with parsing, serialization, parent/display logic, extracts wire-normalization into `item_wire.rs`, and propagates the new identity model throughout reducers, ranking, routing, HTML, and tests, replacing `CanonicalItemUrl` across the project. Side B adds valuable Reddit OAuth support and a UUID-centric account-linking flow with provider linking and trust-weight updates, but it is a feature-focused authentication enhancement rather than the broad foundational identity and API refactor in Side A.