fix #26971: Seek now works after repeat

#26971: Seq::seek(int) should get a uticks, not ticks.
#26966: When we press "Play repeats" button, MuseScore updates current cs->_repeatList, but doesn't update MIDI event list. So, if we disable "Play repeats" MuseScore still plays the old events list (with unwounded repeats). Just needed to send a signal to update events when button pressed.