openai/gpt-chat-latest → A (3:2)

Side A introduces a reusable URL canonicalization subsystem (`server/src/url_rules/`), converts `ItemId` to canonical full URLs, centralizes parsing/parent/breadcrumb logic, and updates projection and Reddit handling to consistently normalize persisted IDs. Side B is a sweeping API refactor that replaces many endpoints with a single RPC layer and room-scoped commands, but much of the patch is code movement and interface consolidation rather than new core behavior, making A's normalization design and identity fixes more foundational and durable.