feat: Add DownloadableProduct model with relations

app/Models/DownloadableProduct.php

@@ -0,0 +1,21 @@
+<?php
+
+namespace App\Models;
+
+use Illuminate\Database\Eloquent\Model;
+use Illuminate\Database\Eloquent\Relations\BelongsTo;
+
+class DownloadableProduct extends Model
+{
+    protected $fillable = [
+        'product_id',
+        'file_url',
+        'download_limit',
+        'expiration_time',
+    ];
+
+    public function product(): BelongsTo
+    {
+        return $this->belongsTo(Product::class, 'product_id');
+    }
+}