`declared_bpm` defaults to 120 when a track sets no setcps, which is right for
the driver — the OLED has to breathe at some rate — and wrong for a picker.
221 of the 703 tracks declare no setcps at all, so a third of the cards were
showing a confident 120 that came from nowhere. That is the worst shape a
wrong number can take: plausible, and load-bearing for the arc he is about to
order tonight.

Now the generator passes default=0 and those cards read "inherits bpm", which
is not a gap but the actual behaviour — a track with no setcps runs at whatever
tempo the previous one left behind, and for building a ramp that is worth
knowing. They sort last on the BPM axis, since they have no place on a ramp
until you decide what they inherit.