feat(domain): Product entity + 5 domain exceptions (PRD-002)

src/api/SIGCM2.Domain/Exceptions/ProductNotFoundException.cs

@@ -0,0 +1,15 @@
+namespace SIGCM2.Domain.Exceptions;
+
+/// <summary>
+/// Thrown when a requested Product does not exist. → HTTP 404
+/// </summary>
+public sealed class ProductNotFoundException : DomainException
+{
+    public int ProductId { get; }
+
+    public ProductNotFoundException(int id)
+        : base($"El producto con id={id} no existe.")
+    {
+        ProductId = id;
+    }
+}