fix(middleware): create missing PreventAccessFromTenantDomains middleware

app/Http/Middleware/PreventAccessFromTenantDomains.php

@@ -0,0 +1,20 @@
+<?php
+
+namespace App\Http\Middleware;
+
+use Closure;
+use Illuminate\Http\Request;
+use Stancl\Tenancy\Tenancy;
+
+class PreventAccessFromTenantDomains
+{
+    public function handle(Request $request, Closure $next)
+    {
+        // 如果租戶已初始化 (代表是從租戶域名存取)，則禁止訪問 Landlord 路由
+        if (tenancy()->initialized) {
+            abort(404);
+        }
+
+        return $next($request);
+    }
+}