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

Deployment/conf_templates/master.conf

@@ -282,9 +282,9 @@
 # watchdog_orchestrator.sh — NOT launched here.
     ARRAY_START_SCRIPTS=(
         "Transcodes/ramdisk_setup.sh"                 # creates ramdisk + symlink before Emby starts
-        "unRAID_Essentials/docker_syslog_filter.sh"   # suppress veth noise before logs fill
-        "unRAID_Essentials/php_fpm_max_children.sh"   # WebGUI performance tuning
-        "unRAID_Essentials/inotify_tuning.sh"         # bump inotify limits — containers miss events if exhausted
+        "System_Essentials/docker_syslog_filter.sh"   # suppress veth noise before logs fill
+        "System_Essentials/php_fpm_max_children.sh"   # WebGUI performance tuning
+        "System_Essentials/inotify_tuning.sh"         # bump inotify limits — containers miss events if exhausted
         "Docker_Essentials/docker_network_connect.sh" # ensure networks exist + connect containers
         "Fallback/fallback.sh"                        # mutual failover — continuous
     )
@@ -294,10 +294,10 @@
 # Run sequentially (foreground) — each must complete before the next starts.
 # Order matters: user scripts first (prevents new ops), then data movement, then containers.
     ARRAY_STOP_SCRIPTS=(
-        "unRAID_Essentials/user_scripts_stop.sh"        # stop background scripts before they start new ops
+        "System_Essentials/user_scripts_stop.sh"        # stop background scripts before they start new ops
         "Fallback/fallback.sh --stop"                   # gracefully stop fallback (not caught by user_scripts_stop)
-        "unRAID_Essentials/rsync_stop.sh --rsync-only"  # kill rsync; skip container recovery (handled below)
-        "unRAID_Essentials/mover_stop.sh"               # stop mover after rsync (they conflict on same files)
+        "System_Essentials/rsync_stop.sh --rsync-only"  # kill rsync; skip container recovery (handled below)
+        "System_Essentials/mover_stop.sh"               # stop mover after rsync (they conflict on same files)
         "Docker_Essentials/docker_container_stop.sh"    # stop all containers last
     )
 
@@ -393,7 +393,7 @@
     WEEKLY_MAINTENANCE_SCRIPTS=(
         "Docker_Essentials/docker_weekly_restart.sh"    # weekly container restarts after sync
         "Docker_Essentials/docker_update_remaining.sh"  # pull updates for all other containers
-        "unRAID_Essentials/clear_logs.sh"               # purge aged logs — Sunday only, low priority
+        "System_Essentials/clear_logs.sh"               # purge aged logs — Sunday only, low priority
         "Media/playback_aware_lidarr_discovery.sh"      # behavior-driven music discovery using weekly Emby playback history
         "Media/playback_aware_radarr_discovery.sh"      # behavior-driven movie discovery using TMDB recommendations
         "Media/playback_aware_sonarr_discovery.sh"      # behavior-driven TV discovery using TMDB recommendations