feat(mq_editor): movable inner bezier control points + clamp() refactor

- P1/P2 in amp editor now draggable horizontally; t0<t1<t2<t3 enforced
- Add clamp() to utils.js; replace all Math.max/min clamping patterns
- Cursor hints: move for P1/P2, ns-resize for P0/P3
- Remove test_fft.html
- Docs: Delete key, style.css/utils.js in architecture, bezier editor section

handoff(Claude): inner control points done, clamp() adopted everywhere

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

1 files changed, 4 insertions, 2 deletions

diff --git a/tools/mq_editor/utils.js b/tools/mq_editor/utils.js
index 2c6b2f5..ed34b8e 100644
--- a/tools/mq_editor/utils.js
+++ b/tools/mq_editor/utils.js
@@ -8,7 +8,7 @@ function evalBezier(curve, t) {
   const dt = curve.t3 - curve.t0;
   if (dt <= 0) return curve.v0;
   let u = (t - curve.t0) / dt;
-  u = Math.max(0, Math.min(1, u));
+  u = clamp(u, 0, 1);
   const u1 = (curve.t1 - curve.t0) / dt;
   const u2 = (curve.t2 - curve.t0) / dt;
   const d0 = (-u1) * (-u2) * (-1);
@@ -29,7 +29,7 @@ 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));
+  u = clamp(u, 0, 1);
   const u1 = (curve.t1 - curve.t0) / dt;
   const u2 = (curve.t2 - curve.t0) / dt;
   const d0 = (-u1) * (-u2) * (-1);
@@ -45,6 +45,8 @@ function evalBezierAmp(curve, t) {
   return l0 * curve.a0 + l1 * curve.a1 + l2 * curve.a2 + l3 * curve.a3;
 }
 
+function clamp(v, lo, hi) { return v < lo ? lo : v > hi ? hi : v; }
+
 // Get canvas-relative {x, y} from a mouse event
 function getCanvasCoords(e, canvas) {
   const rect = canvas.getBoundingClientRect();