fix(mq_editor): fuse spread_above/below into single spread param

Asymmetric spread offset the pitch center. Replace with a single
symmetric `spread` in harmonics config. autodetectSpread now returns
max(above, below). Update all defaults, UI, comments, and README.

handoff(Gemini): spread is now a single param; no compat shims.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

1 files changed, 3 insertions, 4 deletions

diff --git a/tools/mq_editor/viewer.js b/tools/mq_editor/viewer.js
index 1ed609c..c841acb 100644
--- a/tools/mq_editor/viewer.js
+++ b/tools/mq_editor/viewer.js
@@ -304,12 +304,11 @@ class SpectrogramViewer {
     const {ctx} = this;
     const curve    = partial.freqCurve;
     const harm     = partial.harmonics || {};
-    const sa       = harm.spread_above != null ? harm.spread_above : 0.02;
-    const sb       = harm.spread_below != null ? harm.spread_below : 0.02;
+    const spread   = harm.spread != null ? harm.spread : 0.02;
     const decay    = harm.decay        != null ? harm.decay        : 0.0;
     const freqMult = harm.freq_mult    != null ? harm.freq_mult    : 2.0;
 
-    const {upper, lower} = buildBandPoints(this, curve, sa, sb);
+    const {upper, lower} = buildBandPoints(this, curve, spread, spread);
     if (upper.length < 2) return;
 
     const savedAlpha = ctx.globalAlpha;
@@ -379,7 +378,7 @@ class SpectrogramViewer {
         }
 
         // Spread band fill + boundary dashes
-        const {upper: hu, lower: hl} = buildBandPoints(this, curve, sa, sb, hRatio);
+        const {upper: hu, lower: hl} = buildBandPoints(this, curve, spread, spread, hRatio);
         if (hu.length >= 2) {
           ctx.beginPath();
           ctx.moveTo(hu[0][0], hu[0][1]);