7.5.0

Needs PHP 8.3 or newer. Download both assets, keep the binary
named wback-7.5.0 so the checksum matches, and verify with
sha256sum --ignore-missing -c SHA256SUMS before installing it.
See the README for the .env it then needs.

Added

• app:validate --unattended, for a run nobody is watching. Two of the checks
  are only worth their cost when someone looks at where the message landed — the
  sweep that writes a record at every log level, and the run summary test post —
  and a deploy gate fires both into an operations channel with nobody having
  asked. The flag suppresses those two and nothing else: the rclone remote
  checks still go out, because a remote that has stopped responding is what an
  automated gate exists to surface. Both report as skips rather than
  disappearing, and the flag is never the default — forgetting it costs some
  channel noise you can delete, whereas defaulting it on would cost every future
  run its proof of delivery, silently.
• The logging section now says how many records the Slack channel should have
  taken, and at which levels — posted 3 records at critical and above: critical, alert, emergency. The sweep is the only thing that proves the webhook URL and
  LOG_SLACK_LEVEL are both right, since neither can be checked from the sending
  end, and that only works if you know what number to expect. It also reports a
  slack channel sitting in the stack with no webhook to post to, which previously
  looked identical to a working one.