openai/gpt-chat-latest → A (4:1)

Side A replaces the previous ad hoc URL normalization pipeline with a new graph-based canonicalization API (`graph`/`parse`), rewires `canonicalize_raw`, breadcrumbs, and parent resolution to use it, and updates the module structure and documentation to reflect the new semantic model. Side B is a focused UI behavior fix that changes sibling navigation so each unranked sibling becomes its own group and adds a regression test, but its impact is limited compared with the architectural replacement in the URL handling code.