Structural reorganization: watchdog taxonomy + server_reboot integration

Watchdog renames and moves:
  system_watchdog.sh → stability_watchdog.sh (last line of defense — reboots)
  storage_watchdog.sh → Watchdogs/System/storage_watchdog.sh
  webgui_restart.sh → Watchdogs/System/webgui_watchdog.sh (renamed to match folder convention)

New thin orchestrator:
  Watchdogs/system_watchdog.sh — runs SYSTEM_WATCHDOG_SCRIPTS from master.conf
  Sits between docker_watchdog and stability_watchdog in the orchestrator tier chain
  System/ subfolder is the growth seam for future system component watchdogs

master.conf:
  WATCHDOG_ORCHESTRATOR_SCRIPTS updated — storage removed, system_watchdog added as tier
  SYSTEM_WATCHDOG_SCRIPTS array added — storage + webgui

server_reboot.sh:
  Calls array_stopping.sh before VM shutdown for guaranteed safe array stop
  Removed raw rc.docker stop and exit trap — orchestrator owns container shutdown

common.sh

@@ -1322,7 +1322,7 @@ acquire_lock() {
             else
                 error "Another instance of $script_name is already running (PID $existing_pid) — exiting"
                 case "$script_name" in
-                    fallback|transcode_management|daily_sync_maintenance|system_watchdog)
+                    fallback|transcode_management|daily_sync_maintenance|stability_watchdog)
                         notify "$script_name lock collision on $(hostname) — concurrent instance detected" "$script_name" "warning"
                         ;;
                 esac