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/System/network_watchdog.sh

@@ -112,7 +112,7 @@ 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"

Watchdogs/System/webgui_watchdog.sh

@@ -104,7 +104,7 @@ 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"
@@ -132,16 +132,16 @@ if [[ "$SHOW_STATUS" == true ]]; then
         echo "  $ICON_ERROR  WebGUI:    NOT responding"
     fi
 
-    pgrep -x nginx >/dev/null 2>&1 && \
+    platform_is_service_running nginx && \
         echo "  $ICON_SUCCESS nginx:     running ✅" || \
         echo "  $ICON_ERROR  nginx:     NOT running"
 
-    pgrep -f "php-fpm" >/dev/null 2>&1 && \
+    platform_is_service_running php-fpm && \
         FPM_COUNT=$(pgrep -fc "php-fpm" 2>/dev/null || echo "?") && \
         echo "  $ICON_SUCCESS php-fpm:   running ($FPM_COUNT workers) ✅" || \
         echo "  $ICON_ERROR  php-fpm:   NOT running"
 
-    pgrep emhttpd >/dev/null 2>&1 && \
+    platform_is_service_running emhttp && \
         echo "  $ICON_SUCCESS emhttp:    running ✅" || \
         echo "  $ICON_ERROR  emhttp:    NOT running"
     echo "━━━━━━━━━━━━━━━━━━━━━━━"
@@ -185,10 +185,10 @@ if [[ "$DRY_RUN" == true ]]; then
     warn "DRY RUN — would restart nginx"
 else
     warn "Restarting nginx..."
-    if /etc/rc.d/rc.nginx restart >/dev/null 2>&1; then
+    if platform_restart_service nginx; then
         # Verify nginx actually running
         sleep 2
-        if pgrep -x nginx >/dev/null 2>&1; then
+        if platform_is_service_running nginx; then
             warn "nginx restarted ✅"
         else
             error "nginx not running after restart command"
@@ -216,9 +216,9 @@ if [[ "$RECOVERY_OK" == false ]]; then
     if [[ "$DRY_RUN" == true ]]; then
         warn "DRY RUN — would restart php-fpm"
     else
-        if /etc/rc.d/rc.php-fpm restart >/dev/null 2>&1; then
+        if platform_restart_service php-fpm; then
             sleep 2
-            if pgrep -f "php-fpm" >/dev/null 2>&1; then
+            if platform_is_service_running php-fpm; then
                 warn "php-fpm restarted ✅"
             else
                 error "php-fpm not running after restart command"
@@ -249,7 +249,7 @@ if [[ "$RECOVERY_OK" == false ]]; then
     else
         if /usr/local/sbin/emhttp stop >/dev/null 2>&1 && /usr/local/sbin/emhttp start >/dev/null 2>&1; then
             sleep 2
-            if pgrep emhttpd >/dev/null 2>&1; then
+            if platform_is_service_running emhttp; then
                 warn "emhttp restarted ✅"
             else
                 error "emhttp not running after restart command"