openai/gpt-5.3-chat → A (3:2)

Side A introduces a full URL canonicalization system (`url_rules` with parsing, normalization, breadcrumbs, parent logic) and rewires `ItemId` to use it, replacing ad-hoc logic across the codebase—this is a foundational design improvement. Side B fixes an index bug (removing bogus `https://.` parent) and adds GitHub resolver rendering/cards, but these are more feature/UI-oriented and less structurally pervasive than A’s core identity model overhaul.