refactor(mq_editor): unify freq+amp into single bezier curve

freqCurve now carries a0-a3 (amplitude control values) alongside
v0-v3 (frequency). Both components share the same t0-t3 time
parameterization. evalBezierAmp() added to utils.js.
ampCurve removed from partials and synth pipeline.
Amp panel drag now changes only a_i; t is read-only (shared with freq).

handoff(Claude): unified freq/amp bezier done

1 files changed, 13 insertions, 0 deletions

diff --git a/tools/mq_editor/utils.js b/tools/mq_editor/utils.js
index c38b1f5..96d807c 100644
--- a/tools/mq_editor/utils.js
+++ b/tools/mq_editor/utils.js
@@ -13,6 +13,19 @@ function evalBezier(curve, t) {
          u*u*u     * curve.v3;
 }
 
+// Evaluate amplitude component of unified bezier curve at time t
+function evalBezierAmp(curve, t) {
+  const dt = curve.t3 - curve.t0;
+  if (dt <= 0) return curve.a0;
+  let u = (t - curve.t0) / dt;
+  u = Math.max(0, Math.min(1, u));
+  const u1 = 1.0 - u;
+  return u1*u1*u1 * curve.a0 +
+         3*u1*u1*u * curve.a1 +
+         3*u1*u*u  * curve.a2 +
+         u*u*u     * curve.a3;
+}
+
 // Get canvas-relative {x, y} from a mouse event
 function getCanvasCoords(e, canvas) {
   const rect = canvas.getBoundingClientRect();