openai/gpt-chat-latest → B (5:1)

Side B makes a functional change to sibling navigation by placing each unranked sibling into its own navigation group instead of combining all unranked items into one group, and it adds a regression test verifying the new grouping behavior. Side A primarily introduces a planning document and a thin `RouteContext` wrapper around `ThreadNav` with re-exports, which is useful scaffolding but does not materially change project behavior.