Cut a sound to a stretch of its file in its own Sound tab (#343)

A sound asset now opens in a tab that shows its file as a waveform.
Two handles set where the sound starts and ends in the file, and that
stretch is the sample: Play sound, a song item and an instrument's
Sample all play it and nothing else. The file itself is never changed.

- The asset has three new rows: Start (s), End (s) and Edge fade (ms).
  End 0 is the end of the file, the fade is 10 ms by default. Older
  assets have no values and play the whole file as before.
- Every way of playing asks playedSoundOf() for a name instead of the
  file: the file, or <file>#<start>~<end>~<fade> for a cut.
- SoundLibrary makes the cut from the decoded file the first time that
  name plays and ramps each edge inside the file over the fade. Length
  and peaks of a cut are read from the file without a copy.
- Cut buffers can be made again at any time, so the library lets the
  oldest go past 64 Mi samples. A voice holds its buffers itself.
- The tab draws min/max per pixel from 256-sample block peaks, and the
  samples as a line when zoomed in far. Wheel zooms, the middle button
  pans, as in the music tabs. Wave, cut and ruler sit under a mask,
  so a handle panned out of view does not draw over the panels beside.
- Dragging a handle moves that edge, dragging elsewhere spans a new
  stretch. One drag is one undo step for both edges. Whole file puts
  the handles back, Play or Space plays the stretch with a playhead.
- The inspector preview and the Sound FX preview play the cut too, and
  the song lanes draw and repeat it.

Tests:
- Unit: sounds 20, wave-view 8 (new), sound-library 68, plus 258 in
  the touched areas (instrument, song, pattern, inspector, tabs)
- e2e 34 on melektaus-atx: ALL PASSED, 57 checks (7 new)
- Gate on melektaus-atx: CHECK EXIT 0, 253 files, 3936 tests

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/editor/debug/soundHooks.ts

@@ -0,0 +1,44 @@
+import { findAssetOf } from '../../core/model/Project';
+import { playedSoundOf } from '../../core/properties/playedSound';
+import { soundLibrary } from '../../viewport/SoundLibrary';
+import { centreOf, type HookContext } from './hookHelpers';
+
+/** The Sound tab (#343). */
+export function soundHooks({ state, editor }: HookContext) {
+  const { soundEditor } = editor;
+  return {
+    soundTab: {
+      current: () => soundEditor.currentAssetId,
+      info: () => soundEditor.shownInfo,
+      rect: () => soundEditor.canvasRect(),
+      /** Where a second of the file is on screen, at the middle of the wave. */
+      at: (seconds: number) => soundEditor.canvas.secondsToScreen(seconds),
+      /** The stretch between the handles, in seconds; null while the file is not there. */
+      span: () => soundEditor.canvas.shownSpan(),
+      duration: () => soundEditor.canvas.fileDuration(),
+      cursor: () => soundEditor.canvas.cursor,
+      playhead: () => soundEditor.canvas.playhead,
+      playing: () => soundEditor.isPlaying,
+      playButton: () => ({ ...centreOf(soundEditor.playButton), text: soundEditor.playButton.text }),
+      wholeButton: () => ({ ...centreOf(soundEditor.wholeButton), enabled: soundEditor.wholeButton.enabled }),
+      fadeField: () => ({ ...centreOf(soundEditor.fadeField), text: soundEditor.fadeField.value }),
+      /** What a sound asset is played by: its file, or the name of its cut. */
+      played: (assetId: string) => {
+        const asset = findAssetOf(state.project, assetId, 'sound');
+        return asset ? playedSoundOf(state.project, asset) : null;
+      },
+      /** The samples a name plays, cut and faded: their count, rate, and the first and last few of channel 0. */
+      samples: async (name: string) => {
+        const buffer = await soundLibrary.load(name);
+        if (!buffer) return null;
+        const data = buffer.getChannelData(0);
+        return {
+          length: buffer.length,
+          rate: buffer.sampleRate,
+          head: Array.from(data.slice(0, 4)),
+          tail: Array.from(data.slice(-4)),
+        };
+      },
+    },
+  };
+}