Platform adapter: rename System_Essentials, add Plugin/unraid/adapter.sh, wire call sites

- Rename unRAID_Essentials/ → System_Essentials/ (git detects as rename)
- Add Plugin/unraid/adapter.sh: 13 platform_*() functions providing OS-agnostic API
  for storage health, service management, mover, user scripts, notifications,
  disk temps, and platform command validation
- Update load_config.sh: detect PLATFORM (unraid/truenas/unknown), export SCRIPTS_DIR,
  auto-source Plugin/$PLATFORM/adapter.sh after common.sh
- Wire all call sites: replace direct rc.d, pgrep/pkill, var.ini, dynamix.cfg,
  disks.ini, and validate_unraid_cmd calls with platform_*() functions across
  watchdogs, orchestrators, and System_Essentials scripts
- Update all documentation: rename refs, update webgui escalation logic,
  add platform adapter section to Plugin README, update main README with
  portability vision and corrected self-healing stack description

Watchdogs/stability_watchdog.sh

@@ -119,7 +119,7 @@ if [[ "$EUID" -ne 0 ]]; then
     exit 1
 fi
 
-validate_unraid_cmd \
+platform_require_cmd \
     "/usr/local/emhttp/plugins/dynamix/scripts/notify" \
     "" "" \
     "unRAID notify script" || warn "unRAID notify script not found — native notifications disabled"
@@ -302,12 +302,8 @@ check_abort_conditions() {
         fi
     fi
 
-    # Unraid 7.3+: parity state is in var.ini (mdResync != 0 means check/sync in progress)
-    # Older: parity-date.txt contained "progress" — check both for compatibility
-    _md_resync=$(awk -F'"' '/^mdResync=/{print $2}' /var/local/emhttp/var.ini 2>/dev/null)
     _parity_running=false
-    [[ -n "$_md_resync" && "$_md_resync" != "0" ]] && _parity_running=true
-    grep -q "progress" /var/local/emhttp/parity-date.txt 2>/dev/null && _parity_running=true
+    platform_is_maintenance_running && _parity_running=true
     if [[ "$_parity_running" == true ]]; then
         if [[ "$SYS_WATCHDOG_ABORT_ON_PARITY" == true ]]; then
             error "Parity check running — aborting reboot"
@@ -451,7 +447,7 @@ do_reboot() {
     fi
 
     warn "Stopping User Scripts..."
-    pkill -f "/tmp/user.scripts" 2>/dev/null || true
+    platform_stop_user_scripts
 
     warn "Syncing disks..."
     sync
@@ -726,12 +722,12 @@ echo "━━━ $ICON_REBOOT Stability Watchdog — $(date '+%Y-%m-%d %H:%M:%S')
 
     # ── sshd — try restart before escalating ─────────────────────────────────────────────────
     if [[ "$SYS_WATCHDOG_CHECK_SSHD" == true ]]; then
-        if ! pgrep -x sshd >/dev/null 2>&1; then
+        if ! platform_is_service_running sshd; then
             warn "sshd not running — attempting restart..."
             if [[ "$DRY_RUN" == false ]]; then
-                /etc/rc.d/rc.sshd start >/dev/null 2>&1
+                platform_restart_service sshd
                 sleep 3
-                if pgrep -x sshd >/dev/null 2>&1; then
+                if platform_is_service_running sshd; then
                     warn "sshd restarted successfully ✅"
                     reset_strikes "sshd"
                     notify "sshd was down on $(hostname) ($MY_ID) — restarted automatically" \