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

Orchestrators/array_started.sh

@@ -12,10 +12,10 @@
 # Current order (order matters — see below):
 #
 #   ONE-SHOT (run and exit naturally):
-#     unRAID_Essentials/unraid_api_key_renew.sh — re-register Varaverk API key at boot
-#     unRAID_Essentials/inotify_tuning.sh       — raise inotify limits before containers start
-#     unRAID_Essentials/docker_syslog_filter.sh — suppress veth log noise before logs fill
-#     unRAID_Essentials/php_fpm_max_children.sh — WebGUI performance tuning
+#     System_Essentials/unraid_api_key_renew.sh — re-register Varaverk API key at boot
+#     System_Essentials/inotify_tuning.sh       — raise inotify limits before containers start
+#     System_Essentials/docker_syslog_filter.sh — suppress veth log noise before logs fill
+#     System_Essentials/php_fpm_max_children.sh — WebGUI performance tuning
 #     Transcodes/ramdisk_setup.sh               — create tmpfs + symlink before Emby starts
 #     Docker_Essentials/docker_network_connect.sh — ensure networks + container connections
 #
@@ -44,7 +44,7 @@
 #   Root check           — all launched scripts require root
 #   acquire_lock         — prevents duplicate array start launches
 #   detect_hosts()       — MY_ID in notifications
-#   validate_unraid_cmd  — notify validated before use
+#   platform_require_cmd  — notify validated before use
 #   chmod +x auto-fix    — non-executable scripts fixed before launch
 #   Full path on failure — shows exact path for debugging
 #   notify on failures   — alert if any script fails to launch
@@ -74,7 +74,7 @@ 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"