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

Tools/conf_populate.sh

@@ -222,5 +222,5 @@ echo "━━━━━━━━━━━━━━━━━━━━━"
 if [[ "$UPDATED" -gt 0 ]] && [[ "$DRY_RUN" == false ]] && [[ "$NO_PUSH" == false ]]; then
     echo ""
     info "Pushing updated conf to partners..."
-    bash "$SCRIPTS_ROOT/unRAID_Essentials/conf_sync.sh" --push-only "${EXTRA_FLAGS[@]}" || true
+    bash "$SCRIPTS_ROOT/System_Essentials/conf_sync.sh" --push-only "${EXTRA_FLAGS[@]}" || true
 fi