feat(inventory): add refunded_units to inventory model and update related services

database/migrations/2026_09_16_000000_add_refunded_units_to_inventories.php

@@ -0,0 +1,23 @@
+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\Schema;
+
+return new class extends Migration
+{
+    public function up(): void
+    {
+        Schema::table('inventories', function (Blueprint $table): void {
+            $table->unsignedBigInteger('refunded_units')->default(0);
+        });
+
+    }
+
+    public function down(): void
+    {
+        Schema::table('inventories', function (Blueprint $table): void {
+            $table->dropColumn('refunded_units');
+        });
+    }
+};