[FIX] 遷移機台授權為獨立模組：修復變數命名、補齊多語系並強化多租戶數據隔離

app/Models/System/User.php

@@ -31,6 +31,7 @@ class User extends Authenticatable
         'avatar',
         'role',
         'status',
+        'is_admin',
     ];
 
     /**
@@ -51,6 +52,7 @@ class User extends Authenticatable
     protected $casts = [
         'email_verified_at' => 'datetime',
         'password' => 'hashed',
+        'is_admin' => 'boolean',
     ];
 
     /**