feat(api): List + GetById usuarios — handlers, repo, endpoints [UDT-008]

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

@@ -0,0 +1,10 @@
+namespace SIGCM2.Domain.Exceptions;
+
+/// <summary>
+/// Thrown when a user provides an incorrect current password during password change.
+/// </summary>
+public sealed class InvalidOldPasswordException : DomainException
+{
+    public InvalidOldPasswordException()
+        : base("La contraseña actual es incorrecta.") { }
+}