fix: resolve PHPStan static analysis warnings

app/Models/ServerGroup.php

@@ -4,7 +4,17 @@ namespace App\Models;
 
 use Illuminate\Database\Eloquent\Model;
 use Illuminate\Database\Eloquent\Relations\HasMany;
+use Illuminate\Database\Eloquent\Casts\Attribute;
 
+/**
+ * App\Models\ServerGroup
+ *
+ * @property int $id
+ * @property string $name 分组名
+ * @property int $created_at
+ * @property int $updated_at
+ * @property-read int $server_count 服务器数量
+ */
 class ServerGroup extends Model
 {
     protected $table = 'v2_server_group';
@@ -23,4 +33,14 @@ class ServerGroup extends Model
     {
         return Server::whereJsonContains('group_ids', (string) $this->id)->get();
     }
+
+    /**
+     * 获取服务器数量
+     */
+    protected function serverCount(): Attribute
+    {
+        return Attribute::make(
+            get: fn () => Server::whereJsonContains('group_ids', (string) $this->id)->count(),
+        );
+    }
 }