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/ApprovalStep.php

@@ -4,13 +4,16 @@
 
 use App\Models\Members\User;
 use App\Traits\Auditable;
+use App\Traits\BelongsToTenant;
 use Illuminate\Database\Eloquent\Model;
 use Illuminate\Database\Eloquent\Relations\BelongsTo;
+use Illuminate\Database\Eloquent\SoftDeletes;
 
 /**
  * 결재 단계 모델
  *
  * @property int $id
+ * @property int $tenant_id
  * @property int $approval_id
  * @property int $step_order
  * @property string $step_type
@@ -23,7 +26,7 @@
  */
 class ApprovalStep extends Model
 {
-    use Auditable;
+    use Auditable, BelongsToTenant, SoftDeletes;
 
     protected $table = 'approval_steps';
 
@@ -36,6 +39,7 @@ class ApprovalStep extends Model
     ];
 
     protected $fillable = [
+        'tenant_id',
         'approval_id',
         'step_order',
         'step_type',