Split kit and keys; KEYS GEN with MOTIF, 303, TURING, ARP

- genome(seed, salts) now has three parts with their own RNG streams:
  shared (steps, form, swing, arc, layback, fill odds, phase offset),
  kit (density, frame, accent cycle, free snare) and keys (scale/root,
  progression, motif, hocket, bass tone, note lengths, range). ROLL KEYS
  now renews the harmony too; ROLL KIT leaves the keys alone.
- Keys generators share one signature and can fix note lengths:
  MOTIF (the old line), 303 (acid bass, answers in the rests, drone or
  silent pad), TURING (8/16-bit shift register, DRIFT flips bits, 16-bar
  window), ARP (triad/7th arpeggio, roots on kicks).
- Pages: KIT GEN, KEYS GEN; ROLL shows KIT / KEYS; slots keep both gens.
- Flash record v3 (old settings ignored). Bring-up golden checksums updated.
- C port matches; host test and ASan/UBSan pass.

Intended music change: every seed sounds different (genome split, new
generators). Vectors regenerated with npm run vectors; the case grid now
crosses all kit and keys generators, with TURING runs past its window.

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

sim/index.html

@@ -167,7 +167,7 @@ textarea{width:100%;min-height:140px;font:400 11px/1.4 var(--f-mono);background:
     <p class="note" style="margin:8px 0 0">Landscape, laid out like the panel drawing: you sit at the bottom edge, cables leave from the back. The screen is drawn at roughly real size.</p>
     <p class="hint"><b>Track buttons:</b> tap = on ↔ off. Hold = flip it while held (drop a track out, or punch one in).<br>
       <b>Screen map / LEDs:</b> filled = on, hollow center = hit, empty = off, blinking = change waiting for the bar line. Map rows match the button rows.<br>
-      <b>Encoder pages:</b> SEED history · GEN · ROOT · SCALE (AUTO = the seed picks) · BPM · SLOT (push loads, hold push saves) · ROLL (re-roll kit or line) · LEARN (push, press a kit track, hit the pad).<br>
+      <b>Encoder pages:</b> SEED history · KIT GEN · KEYS GEN (MOTIF, 303, TURING, ARP) · ROOT · SCALE (AUTO = the seed picks) · BPM · SLOT (push loads, hold push saves) · ROLL (re-roll kit or keys) · LEARN (push, press a kit track, hit the pad).<br>
       Keys: <kbd>Space</kbd> seed · <kbd>1</kbd>…<kbd>0</kbd> <kbd>-</kbd> tracks · <kbd>←</kbd><kbd>→</kbd> encoder · <kbd>Enter</kbd> push · <kbd>R</kbd> run</p>
   </section>