feat: add webshop offline maintenance mode with admin toggle and red maintenance screen

resources/views/layouts/app.blade.php

@@ -25,6 +25,27 @@
 </head>
 <body class="min-h-full flex flex-col bg-[#FBFBFA] text-slate-800 selection:bg-amber-300 selection:text-slate-900" x-data="{ mobileMenuOpen: false }">
 
+    <!-- Admin Offline Preview Notice -->
+    @if(\App\Models\Setting::get('shop_offline', '0') === '1' && auth()->check() && auth()->user()->isAdmin())
+        <div class="bg-rose-600 text-white px-4 py-2 text-xs font-black flex flex-col sm:flex-row items-center justify-between sticky top-0 z-50 border-b border-rose-700 shadow-lg gap-2">
+            <div class="flex items-center space-x-2">
+                <span class="w-2.5 h-2.5 rounded-full bg-white animate-pulse"></span>
+                <span>⚠️ OFFLINE BEHEERDERS-PREVIEW: De webshop staat momenteel OFFLINE voor gewone bezoekers. Alleen jij als beheerder ziet deze pagina.</span>
+            </div>
+            <div class="flex items-center space-x-2">
+                <a href="{{ route('admin.content.index') }}" class="px-2.5 py-1 rounded-lg bg-rose-700 hover:bg-rose-800 text-white text-[11px] font-bold transition">
+                    Naar Beheer
+                </a>
+                <form action="{{ route('admin.toggle-offline') }}" method="POST" class="inline">
+                    @csrf
+                    <button type="submit" class="px-3 py-1 rounded-lg bg-white text-rose-700 hover:bg-rose-50 text-[11px] font-black shadow transition">
+                        Zet Nu Weer Online
+                    </button>
+                </form>
+            </div>
+        </div>
+    @endif
+
     <!-- Top Announcement Bar (Inschakelbaar en bewerkbaar via Admin) -->
     @if(setting('announcement_enabled', '1') == '1')
         <div class="bg-slate-900 text-white text-xs py-2 px-3 sm:px-4 font-bold border-b border-slate-800">