fix: handle Docker digest-only updates

[oiahoon]

Summary

• recognize Docker digest-only metadata without treating a digest as a semantic version
• report the unchanged Docker tag as both previous and new version when no explicit update type exists
• cover the reported commit metadata and regenerate the checked-in action bundle

Root cause

Dependabot code-formats the old and new digests in the metadata link while dependency-version contains the unchanged image tag. The parser combined the old digest with the tag and incorrectly calculated a major version update.

Validation

• npm test -- --runInBand (57 tests)
• npm run typecheck
• npm run lint
• npm run build (two consecutive builds produced identical output)
• git diff --check

Fixes #726