Fix dead/incorrect vars and consolidate duplicated logic into common.sh

Codebase-wide audit pass: fixed real bugs (SSH hangs missing BatchMode,
local-outside-function no-ops, variable name collisions, a truncated
ratio calc, wrong state-dir path, DARK vs NO_INTERNET drift, and more),
then pulled logic that was duplicated across multiple scripts — arr
cleanup safety gates, docker restart ordering, container maintenance
stop/restart, watchdog state-file helpers, partnership role resolution,
cert expiry checks, remote node discovery, and TMDB discovery scoring —
into common.sh so each now has a single implementation.

Arrs_Stack/upgrade_webhook_handler.sh

@@ -103,13 +103,7 @@ case "$ARR_TYPE" in
 esac
 
 # ── Remote node list ──────────────────────────────────────────────────────────────────────────
-declare -a REMOTE_NODES=()
-for _hv in HOST1 HOST2 HOST3 HOST4 HOST5 HOST6 HOST7 HOST8; do
-    [[ "$_hv" == "$MY_ID" ]] && continue
-    [[ -z "${!_hv:-}" ]] && continue
-    REMOTE_NODES+=("$_hv")
-done
-unset _hv
+discover_remote_nodes
 
 if [[ "${#REMOTE_NODES[@]}" -eq 0 ]]; then
     echo "No remote nodes configured — nothing to push"