Platform-agnostic refactor: eliminate OS-specific hardcodes from core scripts

All bash scripts are now platform-neutral. Unraid-specific paths, commands,
and service checks moved to Plugin/unraid/adapter.sh. Core scripts call
platform_*() functions exclusively — no direct OS paths in runtime logic.

New adapter functions: platform_storage_path, platform_webui_install_path,
platform_scripts_dir_probe_cmd, platform_setup_db_path, platform_storage_healthy,
platform_is_service_enabled, platform_get_temp_thresholds, platform_disk_states_path,
platform_rebuild_container, platform_push_conf, platform_push_setup_state,
platform_get_templates_dir, platform_send_os_notification.

Partnership services stack (Emby/Jellyfin/Seerr/SeerrFin) added as third
onboarding stack alongside auth and arr stacks.

Partnership/partnership_transfer.sh

@@ -126,11 +126,6 @@ if ! command -v docker &>/dev/null; then
     exit 1
 fi
 
-platform_require_cmd \
-    "/usr/local/emhttp/plugins/dynamix/scripts/notify" \
-    "" "" \
-    "unRAID notify script" || warn "unRAID notify script not found — native notifications disabled"
-
 detect_hosts
 
 OWNER_ID="${PARTNERSHIP_OWNER_HOST:-HOST1}"
@@ -291,11 +286,11 @@ if [[ "$DRY_RUN" == false ]]; then
 
     # Push updated master.conf to new owner so both servers agree immediately.
     # master.conf is shared — host-specific credentials live in host*.conf.
+    _probe_cmd=$(platform_scripts_dir_probe_cmd)
     _REMOTE_SD=$(ssh -i "$SSH_KEY" -o ConnectTimeout=5 -o StrictHostKeyChecking=no \
-        "root@${MIRROR_IP}" \
-        "grep -m1 '^SCRIPTS_DIR' /boot/config/plugins/varaverk/varaverk.cfg 2>/dev/null | cut -d= -f2 | tr -d '\"'" \
+        "root@${MIRROR_IP}" "$_probe_cmd" \
         2>/dev/null | tr -d '[:space:]')
-    _REMOTE_SD="${_REMOTE_SD:-/boot/config/plugins/varaverk}"
+    _REMOTE_SD="${_REMOTE_SD:-$SCRIPTS_DIR}"
     scp -i "$SSH_KEY" \
         -o ConnectTimeout="$SSH_TIMEOUT" \
         -o StrictHostKeyChecking=no \