Add docker availability check to all scripts that use docker commands

22 scripts used docker without verifying it's present. Consistent with the
pattern already established in Docker_Essentials scripts. Added after acquire_lock
and before detect_hosts in each script's setup section.

Orchestrators/daily_sync_maintenance.sh

@@ -88,6 +88,11 @@ validate_unraid_cmd \
     "" "" \
     "unRAID notify script" || warn "unRAID notify script not found — native notifications disabled"
 
+if ! command -v docker &>/dev/null; then
+    error "Docker command not found"
+    exit 1
+fi
+
 detect_hosts
 resolve_remote_ip