AlternateScheduleSelector.GetScheduleForDate constructs
new DateTime(year, StartMonth, StartDay) and only recovers from an
out-of-range *day* (rolling to the 1st of the next month); an out-of-range
*month* (e.g. 0 or 13) throws again from inside that recovery path and is
never caught, crashing playout building.
Validate StartMonth/EndMonth (1..12) and StartDay/EndDay (1..31) on both
PUT /api/playouts/{id}/alternate-schedules and PUT /api/playouts/{id}/templates
whenever an item sets LimitToDateRange, returning 422 before dispatching to
the mediator. Both actions already documented 422 in their ProducesResponseType
metadata.