openai/gpt-chat-latest → A (3:2)

Side A fixes a concrete runtime bug by defining `GITHUB_API_BASE_URL` with a default and normalizing it, preventing a `NameError` when the OAuth callback references the setting. Side B mainly removes a supposedly redundant zero-ratio guard and updates tests to reflect the new behavior (registering items/pairs while skipping zero-weight edges), which is more of a cleanup/behavior adjustment than a clear bug fix.