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, 1 insertions, 1 deletions

diff --git a/tools/mq_editor/mq_extract.js b/tools/mq_editor/mq_extract.js
index 18897fb..42215d3 100644
--- a/tools/mq_editor/mq_extract.js
+++ b/tools/mq_editor/mq_extract.js
@@ -451,7 +451,7 @@ function trackIsoContour(stftCache, seedTime, seedFreq, params) {
   }
 
   const seedFrame = stftCache.getFrameAtIndex(seedFrameIdx);
-  const seedBin   = Math.max(1, Math.min(halfBins - 2, Math.round(seedFreq / binHz)));
+  const seedBin   = clamp(Math.round(seedFreq / binHz), 1, halfBins - 2);
   const targetSq  = seedFrame.squaredAmplitude[seedBin];
   if (targetSq <= 0) return null;
   const targetDB  = 10 * Math.log10(targetSq);