The count-in now speaks the exercise name at 5s left, leaves the 4s
beat silent so a long name can finish, then counts down — "in three,
two, one, Go!" (it previously counted up from 4s). Timed work sets
get a mirrored count-out: "<Exercise> ends." at 5s, the same buffer
and countdown, and silence at zero where the rest buzz marks the
boundary; the final "one" releases the audio duck.
Claude-Session: https://claude.ai/code/session_012qw2itfzKyEJ1HpsFt8Ex4