ComfyUI version listing + nightly current fix

[benceruleanlu]

Summary

• parse and sort ComfyUI semver tags descending, expose a capped list of versions (nightly + current describe + top semvers), and derive latest_tag from the highest semver
• treat the default-branch HEAD as nightly for the current label when it is not exactly on a tag, while preserving exact tags as the current label
• stable updates now look up the latest tag ref, skip if already on that commit, and log when the tag ref cannot be found