refactor: [approval] SAM API 규칙 준수 코드 리뷰 반영

- ApprovalStep에 BelongsToTenant, SoftDeletes 추가 (마이그레이션 포함)
- ApprovalForm, ApprovalDelegation에 ModelTrait 추가 (중복 scopeActive 제거)
- ApprovalDelegation에 Auditable 추가
- 모든 결재 액션에 FormRequest 적용 (approve, cancel, hold, preDecide)
- 위임 CRUD에 DelegationStoreRequest, DelegationUpdateRequest 적용
- ApprovalStep 생성 시 tenant_id 포함

app/Models/Tenants/ApprovalForm.php

@@ -5,6 +5,7 @@
 use App\Models\Members\User;
 use App\Traits\Auditable;
 use App\Traits\BelongsToTenant;
+use App\Traits\ModelTrait;
 use Illuminate\Database\Eloquent\Model;
 use Illuminate\Database\Eloquent\Relations\BelongsTo;
 use Illuminate\Database\Eloquent\Relations\HasMany;
@@ -26,7 +27,7 @@
  */
 class ApprovalForm extends Model
 {
-    use Auditable, BelongsToTenant, SoftDeletes;
+    use Auditable, BelongsToTenant, ModelTrait, SoftDeletes;
 
     protected $table = 'approval_forms';
 
@@ -100,14 +101,6 @@ public function updater(): BelongsTo
     // 스코프
     // =========================================================================
 
-    /**
-     * 활성 양식만
-     */
-    public function scopeActive($query)
-    {
-        return $query->where('is_active', true);
-    }
-
     /**
      * 특정 카테고리
      */