cloud-sync: liveness check + sync on boot and shutdown

[maxengel]

Summary

Add a remote liveness check and trigger cloud sync automatically on boot (pull latest) and shutdown (push latest), so devices stay current without manual Tools actions.

Scope

• Liveness check: confirm network is up and the remote is reachable (e.g. rclone lsd <remote>); skip gracefully and log when offline.
• Boot: restore/pull latest saves before play.
• Shutdown: back up/push latest saves; must complete before network teardown.
• Wire via systemd (a boot oneshot + correct shutdown ordering) calling the existing scripts.

Considerations

• Boot delay budget; shutdown race with network down.
• Interacts with auto-save-after-exit, bisync, and conflict resolution (see related backlog issues).

Related: bisync, conflict resolution, system-backup revamp.