v1.43.0

Timer: pick the part of your beat sound that plays (v1.43.0)

The beat opener's MY SOUND gains the waveform picker the owner asked
for, modelled on Instagram's audio trimmer: drag a window over the
uploaded sound to choose the part that plays on every cut, capped at two
beats so the selection is exactly what plays, and preview it with PLAY.
A 1.5 s keyboard hit now plays 1.5 s, and a long sustained tone gives up
just the stretch that's wanted. The uploaded sound now lasts one visit:
cleared on app start, page reload and opening the countdown, so a sound
from a previous session never turns up.

Ordinary countdowns are byte-identical to v1.41.0, golden passes, 621
smoke checks. The PLAY preview's audio was verified by state only; it
could not be listened to here.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>