fix(alarmas): scope schedule-skip exceptions to skipNext only

ExcepcionAlarma._esValida matched ANY exception tipo against an
occurrence, treating it as a user skip. Only the 'skipNext' tipo
existed until now, but the next commits reuse the same model to
record scheduling-reliability failures per alarm (so the alarms list
can surface them via ultimaExcepcionPara) -- without this guard, a
recorded failure would be silently treated as if the user asked to
skip that occurrence, corrupting scheduling. Adds tipo constants to
ExcepcionAlarma for the upcoming failure kinds.

lib/servicios/servicio_programacion_alarmas.dart

@@ -150,9 +150,15 @@ class ServicioProgramacionAlarmas {
     if (!alarma.sonarEnVacaciones && estaEnVacaciones(candidato, vacaciones)) {
       return false;
     }
+    // Only a deliberate user skip ever removes a candidate occurrence.
+    // Reliability-failure records share this same list/model (so the alarms
+    // list can surface them per-alarm via `ultimaExcepcionPara`), but they
+    // must never be mistaken for a skip — that would silently jump the
+    // alarm to its NEXT occurrence instead of just flagging the failed one.
     return !excepciones.any(
       (excepcion) =>
           excepcion.alarmaId == alarma.id &&
+          excepcion.tipo == ExcepcionAlarma.tipoSaltoSiguiente &&
           _mismaEjecucion(excepcion.ejecucion, candidato),
     );
   }