feat(cart): implement cart management with add, update, and remove item functionalities

app/Domains/Cart/Resources/CartResource.php

@@ -0,0 +1,40 @@
+<?php
+
+namespace App\Domains\Cart\Resources;
+
+use Illuminate\Http\Request;
+use Illuminate\Http\Resources\Json\JsonResource;
+
+/**
+ * @mixin \App\Domains\Cart\Models\Cart
+ */
+class CartResource extends JsonResource
+{
+    /**
+     * @return array<string, mixed>
+     */
+    public function toArray(Request $request): array
+    {
+        $items = $this->resource->relationLoaded('items')
+            ? $this->resource->getRelation('items')
+            : collect();
+
+        $subtotal = $items->reduce(
+            fn (float $carry, $item): float => $carry + ((float) ($item->variant?->precio ?? 0) * $item->cantidad),
+            0.0,
+        );
+
+        return [
+            'id' => $this->id,
+            'tenant_codigo' => $this->tenant_codigo,
+            'status' => $this->status ?? 'active',
+            'items' => CartItemResource::collection($items),
+            'subtotal' => $this->formatMoney($subtotal),
+        ];
+    }
+
+    protected function formatMoney(float|int|string|null $amount): string
+    {
+        return number_format((float) ($amount ?? 0), 2, '.', '');
+    }
+}