feat(生產/庫存): 實作生產管理模組與批號追溯功能

app/Models/ProductionOrderItem.php

@@ -0,0 +1,47 @@
+<?php
+
+namespace App\Models;
+
+use Illuminate\Database\Eloquent\Factories\HasFactory;
+use Illuminate\Database\Eloquent\Model;
+use Illuminate\Database\Eloquent\Relations\BelongsTo;
+
+class ProductionOrderItem extends Model
+{
+    use HasFactory;
+
+    protected $fillable = [
+        'production_order_id',
+        'inventory_id',
+        'quantity_used',
+        'unit_id',
+    ];
+
+    protected $casts = [
+        'quantity_used' => 'decimal:4',
+    ];
+
+    /**
+     * 所屬生產工單
+     */
+    public function productionOrder(): BelongsTo
+    {
+        return $this->belongsTo(ProductionOrder::class);
+    }
+
+    /**
+     * 使用的庫存紀錄
+     */
+    public function inventory(): BelongsTo
+    {
+        return $this->belongsTo(Inventory::class);
+    }
+
+    /**
+     * 單位
+     */
+    public function unit(): BelongsTo
+    {
+        return $this->belongsTo(Unit::class);
+    }
+}