feat: G-1 작업지시 관리 API 구현

- 작업지시 테이블 마이그레이션 (work_orders, work_order_items, work_order_bending_details, work_order_issues)
- 작업지시 모델 4개 (WorkOrder, WorkOrderItem, WorkOrderBendingDetail, WorkOrderIssue)
- WorkOrderService 비즈니스 로직 구현
- WorkOrderController REST API 엔드포인트 11개
- FormRequest 검증 클래스 5개
- Swagger API 문서화 완료

API Endpoints:
- GET /work-orders (목록)
- GET /work-orders/stats (통계)
- POST /work-orders (등록)
- GET /work-orders/{id} (상세)
- PUT /work-orders/{id} (수정)
- DELETE /work-orders/{id} (삭제)
- PATCH /work-orders/{id}/status (상태변경)
- PATCH /work-orders/{id}/assign (담당자배정)
- PATCH /work-orders/{id}/bending/toggle (벤딩토글)
- POST /work-orders/{id}/issues (이슈등록)
- PATCH /work-orders/{id}/issues/{issueId}/resolve (이슈해결)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

app/Models/Production/WorkOrderItem.php

@@ -0,0 +1,62 @@
+<?php
+
+namespace App\Models\Production;
+
+use App\Models\Items\Item;
+use Illuminate\Database\Eloquent\Model;
+use Illuminate\Database\Eloquent\Relations\BelongsTo;
+
+/**
+ * 작업지시 품목 모델
+ */
+class WorkOrderItem extends Model
+{
+    protected $table = 'work_order_items';
+
+    protected $fillable = [
+        'work_order_id',
+        'item_id',
+        'item_name',
+        'specification',
+        'quantity',
+        'unit',
+        'sort_order',
+    ];
+
+    protected $casts = [
+        'quantity' => 'decimal:2',
+        'sort_order' => 'integer',
+    ];
+
+    // ──────────────────────────────────────────────────────────────
+    // 관계
+    // ──────────────────────────────────────────────────────────────
+
+    /**
+     * 작업지시
+     */
+    public function workOrder(): BelongsTo
+    {
+        return $this->belongsTo(WorkOrder::class);
+    }
+
+    /**
+     * 품목
+     */
+    public function item(): BelongsTo
+    {
+        return $this->belongsTo(Item::class);
+    }
+
+    // ──────────────────────────────────────────────────────────────
+    // 스코프
+    // ──────────────────────────────────────────────────────────────
+
+    /**
+     * 정렬 순서
+     */
+    public function scopeOrdered($query)
+    {
+        return $query->orderBy('sort_order');
+    }
+}