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, 3 insertions, 3 deletions

diff --git a/tools/mq_editor/viewer.js b/tools/mq_editor/viewer.js
index d7b5ac1..1bc5fc9 100644
--- a/tools/mq_editor/viewer.js
+++ b/tools/mq_editor/viewer.js
@@ -109,7 +109,7 @@ class SpectrogramViewer {
 
   // DB value -> normalized intensity [0..1], relative to cache maxDB over 80dB range
   normalizeDB(magDB, maxDB) {
-    return Math.max(0, Math.min(1, (magDB - (maxDB - 80)) / 80));
+    return clamp((magDB - (maxDB - 80)) / 80, 0, 1);
   }
 
   // Partial index -> display color
@@ -643,8 +643,8 @@ class SpectrogramViewer {
       const {x, y} = getCanvasCoords(e, canvas);
 
       if (this.dragState) {
-        const t = Math.max(0, Math.min(this.t_max, this.canvasToTime(x)));
-        const v = Math.max(this.freqStart, Math.min(this.freqEnd, this.canvasToFreq(y)));
+        const t = clamp(this.canvasToTime(x), 0, this.t_max);
+        const v = clamp(this.canvasToFreq(y), this.freqStart, this.freqEnd);
         const partial = this.partials[this.selectedPartial];
         const i = this.dragState.pointIndex;
         partial.freqCurve['t' + i] = t;