feat(copycat): melodic rework — demucs onset analysis, controller mapping

NTO La Clé des Champs algoraoke:
- Bass: dropped to Bb1/F2 (demucs confirmed 58-87Hz range)
- Bass answer: V chord tones A2→C2→F2 (onset analysis, not Eb Db C)
- Answer timing: quarter notes over 2 bars (was 83ms triplets, now 500ms)
- Arp: simplified to <[bf4 f4]*8!6 [ef4 gf4]*8!2> (no note-flip)
- Cello d7: reworked as sustained counter-melody (5ths/3rds), not bass double
- Drums: added sometimesBy knob control (^30 clap flam, ^32 hat roll, ^52 legato)
- d8 breaks: full treatment (^92 ply, ^60 chop mode, ^36/^56 break switch)
- Header: rewritten with demucs spectral evidence and onset analysis data
- SC: s.volume=2 + StageLimiter.activate for output levels

start_and_midi.scd

@@ -174,6 +174,7 @@ s.waitForBoot {
 	};
 };
 
-s.volume = 1;
+s.volume = 2; // +6dB — SuperDirt defaults are conservative
+StageLimiter.activate; // BatLib safety limiter on master out
 s.latency = 0.3; // increase this if you get "late" messages
 );