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, 2 insertions, 2 deletions

diff --git a/tools/mq_editor/app.js b/tools/mq_editor/app.js
index 9b05789..dd0a24f 100644
--- a/tools/mq_editor/app.js
+++ b/tools/mq_editor/app.js
@@ -4,13 +4,13 @@
 function k1ToHz(k, sr) {
   if (k >= 1.0) return sr / 2;
   const cosW = (2 - 2*k - k*k) / (2*(1 - k));
-  return Math.acos(Math.max(-1, Math.min(1, cosW))) * sr / (2 * Math.PI);
+  return Math.acos(clamp(cosW, -1, 1)) * sr / (2 * Math.PI);
 }
 // HP: y[n] = k*(y[n-1]+x[n]-x[n-1])  => -3dB from peak at cos(w) = 2k/(1+k²)
 function k2ToHz(k, sr) {
   if (k >= 1.0) return 0;
   const cosW = 2*k / (1 + k*k);
-  return Math.acos(Math.max(-1, Math.min(1, cosW))) * sr / (2 * Math.PI);
+  return Math.acos(clamp(cosW, -1, 1)) * sr / (2 * Math.PI);
 }
 function fmtHz(f) {
   return f >= 1000 ? (f/1000).toFixed(1) + 'k' : Math.round(f) + 'Hz';