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

Plugin/README-Plugin.md

@@ -33,7 +33,8 @@ no separate monitoring stack, no third-party dashboards.
 Plugin/
 ├── dev_install.sh             # One-time developer setup: symlinks plugin into web server
 ├── Icons/                     # Source icon assets (1024px master files)
-└── unraid/                    # The Unraid plugin application
+└── unraid/                    # The Unraid platform adapter + plugin application
+    ├── adapter.sh             # Platform adapter — provides platform_*() API to all scripts
     ├── Varaverk.page          # Main plugin entry point (Tasks menu)
     ├── VaraverkSettings.page  # Unraid Settings → Other Settings entry
     ├── api/                   # PHP API endpoints (called by JS via fetch)
@@ -45,6 +46,10 @@ Plugin/
     ├── js/                    # Frontend JavaScript
     ├── pages/                 # Per-tab page includes (monitor, scheduler, docker, ...)
     └── run_job.sh             # Script runner invoked by the Scheduler
+
+# Future platform adapters follow the same structure:
+# Plugin/truenas/adapter.sh   — TrueNAS adapter (future)
+# Plugin/ubuntu/adapter.sh    — Ubuntu/Debian adapter (future)
 ```
 
 ---
@@ -74,6 +79,37 @@ so behaviour stays consistent without a shell dependency.
 
 ---
 
+
+## ━━━ THE PLATFORM ADAPTER ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
+
+`Plugin/unraid/adapter.sh` is the Unraid platform adapter. It is sourced automatically
+by `load_config.sh` whenever `PLATFORM=unraid` is detected (via `/etc/unraid-version`).
+
+Every bash script in the ecosystem calls `platform_*()` functions instead of OS-specific
+commands directly. The adapter translates those calls into Unraid-specific implementations.
+
+```
+platform_storage_healthy          # is the array up and shfs mounted?
+platform_is_maintenance_running   # parity check or sync in progress?
+platform_is_service_running       # is a named service process alive?
+platform_restart_service          # restart via rc.d (Unraid) or systemctl (future)
+platform_stop_service             # stop a named service
+platform_is_mover_running         # Unraid mover active?
+platform_get_mover_pid            # PID of the mover process
+platform_stop_user_scripts        # kill Unraid user.scripts background jobs
+platform_send_os_notification     # dynamix notify (Unraid) or equivalent
+platform_get_disk_states          # reads disks.ini (Unraid) or equivalent
+platform_get_temp_thresholds      # reads dynamix.cfg (Unraid) or equivalent
+platform_is_service_enabled       # docker.cfg / domain.cfg enabled check
+platform_require_cmd              # verify a platform command exists
+```
+
+**Adding a new platform:** Create `Plugin/<platform>/adapter.sh` implementing the same
+function names. `load_config.sh` detects the OS at runtime and sources the correct adapter.
+No other files need changing.
+
+---
+
 ## ━━━ UNRAID INTEGRATION POINTS ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
 
 | File | Where it appears in Unraid |