Polish before first GitHub push: consistent adapter usage and naming

stability_watchdog.sh mover check now uses platform_is_mover_running()
instead of raw pgrep, matching server_reboot.sh.

check_unraid_version_parity() renamed to check_os_version_parity() —
the function internals were already platform-neutral after the adapter
refactor; the name was the last Unraid artifact.

Rsync/rsync.sh

@@ -52,7 +52,7 @@
 #   Written at offboard — prevents stale access after a partnership ends.
 #
 # Version Parity
-#   check_unraid_version_parity — refuses sync if servers on incompatible unRAID versions.
+#   check_os_version_parity — refuses sync if servers on incompatible unRAID versions.
 #
 # Remote Health Pre-flights
 #   check_connectivity() — Tailscale IP reachable before any SSH
@@ -248,7 +248,7 @@ else
 fi
 
 # Version parity — refuse if servers on incompatible unRAID versions
-check_unraid_version_parity || exit 1
+check_os_version_parity || exit 1
 
 check_connectivity
 check_remote_rootfs