fix : 모델, BOM 구성 수정

- 설계용 모델, BOM 기능 추가

app/Models/Design/DesignModel.php

@@ -0,0 +1,26 @@
+<?php
+
+namespace App\Models\Design;
+
+use Illuminate\Database\Eloquent\Model;
+use Illuminate\Database\Eloquent\SoftDeletes;
+
+class DesignModel extends Model
+{
+    use SoftDeletes;
+
+    protected $table = 'models';
+
+    protected $fillable = [
+        'tenant_id','code','name','category_id','lifecycle','description','is_active',
+    ];
+
+    protected $casts = [
+        'is_active' => 'boolean',
+    ];
+
+    // 관계: 모델은 여러 버전을 가짐
+    public function versions() {
+        return $this->hasMany(ModelVersion::class, 'model_id');
+    }
+}