openai/gpt-chat-latest → B (4:1)

Side B changes the sibling navigation logic so each unranked sibling is placed into its own navigation group instead of combining all unranked items into a single group, updates the documentation to match the behavior, and adds a regression test verifying the new grouping. Side A is a targeted fix that defines `GITHUB_API_BASE_URL` with a default value to prevent a `NameError`, but it is a much narrower configuration bugfix.