feat(cart): add Cart and CartItem models with item management methods

app/Domains/Cart/Models/CartItem.php

@@ -0,0 +1,46 @@
+<?php
+
+namespace App\Domains\Cart\Models;
+
+use App\Domains\Catalog\Models\ProductVariant;
+use Illuminate\Database\Eloquent\Attributes\Fillable;
+use Illuminate\Database\Eloquent\Factories\HasFactory;
+use Illuminate\Database\Eloquent\Model;
+use Illuminate\Database\Eloquent\Relations\BelongsTo;
+
+#[Fillable([
+    'cart_id',
+    'producto_variante_id',
+    'cantidad',
+])]
+class CartItem extends Model
+{
+    use HasFactory;
+
+    protected $table = 'carrito_items';
+
+    protected function casts(): array
+    {
+        return [
+            'cart_id' => 'integer',
+            'producto_variante_id' => 'integer',
+            'cantidad' => 'integer',
+        ];
+    }
+
+    /**
+     * @return BelongsTo<Cart, $this>
+     */
+    public function cart(): BelongsTo
+    {
+        return $this->belongsTo(Cart::class, 'cart_id');
+    }
+
+    /**
+     * @return BelongsTo<ProductVariant, $this>
+     */
+    public function variant(): BelongsTo
+    {
+        return $this->belongsTo(ProductVariant::class, 'producto_variante_id');
+    }
+}