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, 17 insertions, 1 deletions

diff --git a/tools/mq_editor/README.md b/tools/mq_editor/README.md
index 9435883..6f75a52 100644
--- a/tools/mq_editor/README.md
+++ b/tools/mq_editor/README.md
@@ -95,6 +95,7 @@ Committed partials are prepended to the partial list with full undo support.
 | `C` | Toggle ≋ Contour mode (iso-energy tracking) |
 | `P` | Toggle raw peak overlay |
 | `A` | Toggle mini-spectrum: original ↔ synthesized |
+| `Delete` | Delete selected partial |
 | `Esc` | Exit explore/contour mode · deselect partial |
 | `Ctrl+Z` | Undo |
 | `Ctrl+Y` / `Ctrl+Shift+Z` | Redo |
@@ -104,10 +105,12 @@ Committed partials are prepended to the partial list with full undo support.
 ## Architecture
 
 - `index.html` — UI, playback, extraction orchestration, keyboard shortcuts
+- `style.css` — All UI styles (extracted from inline styles)
 - `editor.js` — Property panel and amplitude bezier editor for selected partials
 - `fft.js` — Cooley-Tukey radix-2 FFT + STFT cache
 - `mq_extract.js` — MQ algorithm: peak detection, forward tracking, backward expansion, bezier fitting
 - `mq_synth.js` — Oscillator bank + two-pole resonator synthesis from extracted partials
+- `utils.js` — Shared helpers: `evalBezier`, `evalBezierAmp`, `clamp`, canvas coordinate utilities
 - `viewer.js` — Visualization: coordinate API, spectrogram, partials, mini-spectrum, mouse/zoom
 
 ### viewer.js coordinate API
@@ -123,6 +126,19 @@ Committed partials are prepended to the partial list with full undo support.
 | `normalizeDB(db, maxDB)` | dB → intensity [0..1] over 80 dB range |
 | `partialColor(p)` | partial index → display color |
 
+## Amplitude Bezier Editor
+
+The bottom panel shows the amplitude envelope for the selected partial as a **Lagrange interpolating curve** through four control points P0–P3.
+
+- **P0, P3** (endpoints): drag vertically to adjust amplitude at the start/end of the partial. Time positions are fixed to `t_start`/`t_end`.
+- **P1, P2** (inner points): drag in **both axes** — vertically for amplitude, horizontally for time position. The ordering constraint `t0 < t1 < t2 < t3` is enforced automatically.
+
+Cursor hints: `ns-resize` for P0/P3, `move` for P1/P2.
+
+All four time and amplitude values are also editable as numbers in the property panel above.
+
+---
+
 ## Post-Synthesis Filters
 
 Global LP/HP filters applied after the oscillator bank, before normalization.
@@ -200,7 +216,7 @@ For a partial at 440 Hz with `spread = 0.02`: `BW ≈ 8.8 Hz`, `r ≈ exp(−πÂ
   - [x] Synthesized STFT cache for FFT comparison
 - [x] Phase 3: Editing UI
   - [x] Partial selection with property panel (freq/amp/synth tabs)
-  - [x] Amplitude bezier drag editor
+  - [x] Amplitude bezier drag editor (P1/P2 horizontally movable, ordering constrained)
   - [x] Synth params with jog sliders (decay, jitter, spread)
   - [x] Auto-spread detection per partial and global
   - [x] Mute / delete partials