A backup under --skip-errors printed its skip errors, then "Finished
successfully.", and exited 0, so a cron wrapper could not tell it from
a complete backup.
Each skipped entry, including a directory the walk could not list, is
now counted as examined and failed. If --skip-errors skipped anything
it could not read or list, the run still keeps its snapshots and
prunes as before, then fails with "Backup completed, but N file(s)
could not be read". A file removed during the run, even before the
walk reaches it, counts once as failed and leaves the exit status
alone; without the flag it no longer stops the backup. Excluded
entries are never counted.
Model: opus-5-5
