feat(API): 작업지시 공정 연동 개선

- WorkOrder 모델에 process_id 추가
- process 관계 추가 (Process 모델)
- 공정별 다중 작업지시 생성 지원
- WorkOrderStoreRequest/UpdateRequest 수정

Co-Authored-By: Claude <noreply@anthropic.com>

app/Http/Requests/WorkOrder/WorkOrderUpdateRequest.php

@@ -4,7 +4,6 @@
 
 use App\Models\Production\WorkOrder;
 use Illuminate\Foundation\Http\FormRequest;
-use Illuminate\Validation\Rule;
 
 class WorkOrderUpdateRequest extends FormRequest
 {
@@ -19,8 +18,8 @@ public function rules(): array
             // 기본 정보
             'sales_order_id' => 'nullable|integer|exists:orders,id',
             'project_name' => 'nullable|string|max:200',
-            'process_type' => ['nullable', Rule::in(WorkOrder::PROCESS_TYPES)],
-            'status' => ['nullable', Rule::in(WorkOrder::STATUSES)],
+            'process_id' => 'nullable|integer|exists:processes,id',
+            'status' => ['nullable', 'in:'.implode(',', WorkOrder::STATUSES)],
             'assignee_id' => 'nullable|integer|exists:users,id',
             'team_id' => 'nullable|integer|exists:departments,id',
             'scheduled_date' => 'nullable|date',