venus-db-backup.sh prune glob crosses lanes — retention 84 total not 84 encrypted; effective 6 days not 7

venus-db-backup.sh prunes with glob venus-prod-*.sql.gz*, matching the LEGACY PLAINTEXT .sql.gz artifacts as well as current .sql.gz.gpg ones. VENUS_DB_BACKUP_KEEP=84 is therefore 84 files across BOTH lanes, not 84 of this lane's. Effective encrypted retention today is 73 files (~6 days), not the 7 days the constant claims — and the lane has been deleting another lane's artifacts as a side effect (25 legacy files; that is what the 'pruned 1 old artifact(s)' journal lines were). Found by bin-venus-cc during VENUS-350 (msimxu8xce2c). Two defects in one: the glob crosses lanes, and the retention promise is silently unmet. Hold until VENUS-350 releases the file.