safeguard: check Docker/VM Manager enabled before acting

common.sh: add is_docker_enabled() and is_vm_manager_enabled() helpers
reading /boot/config/docker.cfg and /boot/config/domain.cfg.

docker_watchdog: exit cleanly if Docker not enabled in Unraid settings.
stability_watchdog: skip Docker daemon check and Docker container stop
if Docker not enabled; skip virsh VM shutdown if VM Manager not enabled.
server_reboot: skip VM shutdown and libvirt stop if VM Manager not enabled.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Watchdogs/docker_watchdog.sh

@@ -240,6 +240,11 @@ acquire_lock
 # detect_hosts() sets MY_ID and aliases all HOST*_WATCHDOG_* arrays
 detect_hosts
 
+if ! is_docker_enabled; then
+    log "Docker not enabled in Unraid settings — skipping cycle"
+    exit 0
+fi
+
 if ! command -v docker >/dev/null 2>&1; then
     error "Docker not found — cannot start watchdog"
     exit 1