feat(mq_editor): partial spectrum viewer — synth+FFT power display

Adds a 200×100 canvas (left of the main spectrum overlay) that shows
the synthesised power spectrum of the selected partial at the time
under the mouse (or playhead).

Pipeline: synthesizeMQ → Hann window → FFT (2048-pt) → dB power bars.
- freqCurve times are shifted so the synthesis window is centred on t
- X-axis: log-frequency (same scale as main view)
- Y-axis: dB, normalised to peak of the synthesised frame
- Cache: {partialIndex, time} → avoids re-synthesis on mouse move;
  bypassed (force=true) from render() so param changes always redraw

handoff(Claude): partial spectrum viewer complete

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

1 files changed, 1 insertions, 0 deletions

diff --git a/tools/mq_editor/style.css b/tools/mq_editor/style.css
index ed518f5..07a404a 100644
--- a/tools/mq_editor/style.css
+++ b/tools/mq_editor/style.css
@@ -39,6 +39,7 @@ button.contour-active { background: #145; border-color: #0cc; color: #aff; }
 /* === Canvas & overlays === */
 #canvas { border: 1px solid #555; background: #000; cursor: crosshair; display: block; flex-shrink: 0; }
 #cursorCanvas, #playheadCanvas { position: absolute; top: 0; left: 0; pointer-events: none; }
+#partialSpectrumViewer { position: absolute; bottom: 10px; right: 420px; width: 200px; height: 100px; background: rgba(30,30,30,.9); border: 1px solid #555; border-radius: 3px; pointer-events: none; }
 #spectrumViewer { position: absolute; bottom: 10px; right: 10px; width: 400px; height: 100px; background: rgba(30,30,30,.9); border: 1px solid #555; border-radius: 3px; pointer-events: none; }
 #keepOverlay { position: absolute; bottom: 10px; left: 10px; background: rgba(30,30,30,.88); border: 1px solid #555; border-radius: 3px; padding: 4px 8px; display: flex; align-items: center; gap: 6px; font-size: 12px; color: #aaa; user-select: none; }
 #keepOverlay input[type="range"] { width: 90px; }