gen: retune for the ADSR fix, and the new instruments in the shipped pieces

[mishan]

Two things for the shipped pieces: a survey of what #337 (env::adsr following its trigger) changed, with retuning where it mattered, and the new instruments where they fit.

The ADSR survey

I rendered every piece for 240 s with the pre-#337 envelope and the current one.

• 16 of 40 are bit-identical.
• 7 differ inaudibly, more than 35 dB down.
• The changes that matter are almost all basslines: sixteenths and octave figures on instruments whose decay is longer than the note. They used to play out the decay; now they release at the note's end, so they came out tighter and 0.6–2.6 dB quieter.

piece	instrument	before the retune	release now	channel vs. original
pearl	bass	-2.6 dB	760 ms	+0.2 dB
seq	bass	-2.1 dB	760 ms	-0.3 dB
sunrise	bass / pulse	-1.6 / -1.0 dB	400 / 390 ms	+0.0 / +0.1 dB
boombox	bass	-1.2 dB	450 ms	+0.2 dB
warehouse	bass	-1.7 dB	450 ms	+0.1 dB
anthem	bass / pluck	-0.6 / -1.0 dB	220 / 360 ms	+0.0 / +0.0 dB
riviera	clav	-1.0 dB	210 ms	+0.1 dB

• Why the release: lengthening the release, rather than the notes, keeps each note's articulation and lets it ring out about as long as the old decay did. Longer notes would turn into slides on these mono basses.
• Left as is: mirrorball's section and round's low pad changed by under 1 dB (short notes on slow attacks) and are left alone.

New instruments

• Glue master: the eight pieces that ended in fx/limiter.dsp (boombox, mirrorball, outrun, pearl, philly, riviera, sunrise, warehouse) now end in fx/glue.dsp. Its ceiling is the old limiter's, and its makeup is set so each piece renders within 0.05 dB of its original level.
• philly: the organ is tonewheel.dsp, with drawbars at the old additive organ's harmonics, through the same rotary with its new drive at 1.
• pearl: the DX electric piano is dx5.dsp. It needed amp 82 to match the old one's level.
• free: the sixth instrument is the tonewheel.
• Each swapped instrument is level-matched to what it replaced, within 0.3 dB.

Left alone on purpose

• sunrise and riviera keep their Solina. Both pieces are about a string machine; the Violins ensemble would change what they are.
• philly's horns stay on brass.dsp. The piece drives its fall knob, which horns.dsp doesn't have.
• ebb's drone stays on organ0. It fades in over 700 ms, and the tonewheel has no attack setting.
• The game-music pieces keep their chip sound.
• No sampled instruments in shipped pieces: a demo shouldn't need a download to make sound.

Testing

• Every changed piece renders with no clipped samples, within 0.05 dB of its original overall level.
• ctest -R "gencheck|dsp|fx" passes.
• 60 s before/after pairs for every changed piece are in the worktree's survey/ folder (not committed).