Add CheckResult (LockPresent, ErrorsFound) and RunCheck. subsetPct>0
passes --read-data-subset N% to limit data reads. Stderr is sniffed
for "Found stale lock"/"locked" to set LockPresent; a non-zero exit
from restic is absorbed as ErrorsFound=true rather than an error so
the caller can always persist last_check_status. Tests cover lock
detection, exit-1 absorption, and subset-arg plumbing.
steve
5e2b88c6dd