guardarAlarma only recomputed proximaEjecucion for the alarm being
saved; every other alarm kept whatever snapshot the last periodic
recalculation left, which can be stale or already past-due. Since
EstadoAlarmas.proximaAlarma just sorts by proximaProgramable, a stale
sibling could wrongly outrank a freshly activated/created/edited
alarm in the "Próxima alarma" panel until the next 1-minute tick.
Extended the same full-list recalculation guardarVacaciones already
did to guardarAlarma, eliminarAlarma, completarEjecucion,
sincronizarEjecucionesNativas, saltarProxima and
posponerEjecucionHasta, via a shared _recalcularLista helper.
