drain: fall back committerDid → ownerDid → repoDid
some knots (notably knot.pdsls.dev) emit refUpdate events with
committerDid: "" — their pushes were silently dropped by the indexer.
falling back to ownerDid / repoDid credits the repo owner, which is
the best attribution we can get when the committer is blank. catches
juliet.paris and the other knot.pdsls.dev residents.
cursor for knot.pdsls.dev has been reset so next cron tick re-drains
from 0 with the new rule.
Co-Authored-By: Claude Opus 4 (1M context) <noreply@anthropic.com>