Add a host-watcher-backed update button on Version & Releases. The container
(no Docker socket) writes an update sentinel; a new root-run systemd unit
(clusev-update.path/.service) runs watch.sh update -> update.sh (git pull +
idempotent install). The sentinel is consumed before running so a persistent
failure can't loop the path unit.
The button only appears once a check finds a newer release, is per-user
throttled (3/10min, auto-expiring) and audited (deploy.update_request); the UI
warns the dashboard is briefly down during the rebuild. install.sh now installs
both the restart and update host units (update unit runs as root for
docker/systemd/apt).
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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