Extract Ladill QR Plus as standalone app at qr.ladill.com.

Utility QR types only (URL, WiFi, link list, business, app download) with
SSO, Billing API integration, public /q resolver, and qr-plus:import for
platform migration. vCard and commerce types stay on the platform.

Co-authored-by: Cursor <cursoragent@cursor.com>

app/Models/QrDocument.php

@@ -0,0 +1,11 @@
+<?php
+
+namespace App\Models;
+
+use Illuminate\Database\Eloquent\Model;
+
+/** Stub — document/file QRs belong to Ladill Transfer, not QR Plus. */
+class QrDocument extends Model
+{
+    protected $guarded = [];
+}