feat: [bending] 절곡품 코드맵/품목매핑/LOT 채번 API 추가

- bending_item_mappings 테이블 마이그레이션
- BendingCodeService: 코드 체계, 품목 매핑, LOT 일련번호 생성
- BendingController: code-map, resolve-item, generate-lot 엔드포인트
- StoreOrderRequest/UpdateOrderRequest: bending_lot validation 추가

app/Models/Production/BendingItemMapping.php

@@ -0,0 +1,33 @@
+<?php
+
+namespace App\Models\Production;
+
+use App\Models\Items\Item;
+use App\Traits\BelongsToTenant;
+use Illuminate\Database\Eloquent\Model;
+use Illuminate\Database\Eloquent\Relations\BelongsTo;
+
+class BendingItemMapping extends Model
+{
+    use BelongsToTenant;
+
+    protected $table = 'bending_item_mappings';
+
+    protected $fillable = [
+        'tenant_id',
+        'prod_code',
+        'spec_code',
+        'length_code',
+        'item_id',
+        'is_active',
+    ];
+
+    protected $casts = [
+        'is_active' => 'boolean',
+    ];
+
+    public function item(): BelongsTo
+    {
+        return $this->belongsTo(Item::class);
+    }
+}