Draw the EQ's curve in its node and a spectrum behind it (#375, #374)

Both were asked for in #367 "for later". The node of a Parametric EQ
now shows its curve in small, and its tab shows what passes the node
while it is seen.

#375, the curve in the node:

- NodeDef has an optional `picture`: a height, and shapes made from
  the settings as plain point lists (guide, area, line). It is
  general, the Parametric EQ is its first user.
- NodeView draws it in a box below the rows, again only when the box
  or the settings change. A drag in the EQ tab changes them, so the
  node follows it live.
- Without a band the box stays, flat on its 0 dB line, so the node
  does not grow at the first band.
- The axes of the curve, `eqCurvePoints` and `fillShapes` move from
  editor/soundfx/eqView to core/soundfx/parametricEq. Tab and node
  draw the sum from the same function.

#374, the spectrum:

- A node marked `tapped` gets a `tap` stage in front of its own
  stages and one behind them when compiled, in a sound FX and in an
  instrument alike. Its id is asset and node, since a copied asset
  keeps its node ids.
- A tap is a gain of 1. SpectrumTaps (new, viewport/spectrum.ts)
  holds the tap of every voice and bus while it plays.
- While the EQ tab is seen, in the tab row or in a window, the taps
  of that node feed one analyser per side (8192 points). Nothing is
  made before a tap of the node plays, so no AudioContext is opened
  early.
- The tab draws both behind the curve, on a scale of 0 to -96 dBFS:
  the sound coming in faint and grey, the sound going on in the
  colour of a sound port. The analyser smooths it, and once the
  sound has gone the sum still hands it silence, so it falls away.
- Once the tab is not seen, Editor.tick lets the analysers go, like
  the meters of the Song tab.
- A tap does nothing to the sound, so `stats().last.stages` leaves it
  out, and a bypassed EQ keeps its taps.

Decided on my own:

- Every sound passing the node counts: Play of the sound FX tab, an
  instrument's keys, a song, a run. The issue proposed that.
- The spectrum has no labels of its own. Its scale is in the wiki.

Tests:

  Gate (melektaus-atx)     275 files, 4247 tests (11 new), EXIT 0
  e2e 34 (melektaus-atx)   ALL PASSED, 98 checks (2 new), twice

Counter-checks, each put back by copy and compared with cmp:

- The node's curve drawn without its bands: 2 unit tests fail.
- The spectrum without the loudest bin between two points: 1 fails.
- SpectrumTaps.stop leaving the taps linked: 1 fails.
- Taps that never feed the analyser: e2e 34 fails in exactly the
  spectrum check (frames 0). Run in the container only.

The screenshots of the second run were looked at: the blip as one
peak behind the curve, and the dip at 4 kHz in the node.

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

src/editor/debug/graphHooks.ts

@@ -1,4 +1,5 @@
 import { NameTransitionCommand } from '../../core/commands/graphCommands';
+import { soundLibrary } from '../../viewport/SoundLibrary';
 import { currentNodePalette } from '../graph/NodePalette';
 import { rectOf } from '../textProbe';
 import { centreOf, snapButton, type HookContext } from './hookHelpers';
@@ -111,6 +112,8 @@ export function graphHooks({ state, editor }: HookContext) {
       }),
       playAt: () => centreOf(editor.soundFxEditor.playButton),
       stopAt: () => centreOf(editor.soundFxEditor.stopButton),
+      /** As the header's Play does, also while the tab is behind another one. */
+      play: () => editor.soundFxEditor.play(),
       /** The header's parameter values, and setting one as its field would. */
       params: () => editor.soundFxEditor.previewValues,
       setParam: (key: string, value: number) => editor.soundFxEditor.setPreviewValue(key, value),
@@ -134,6 +137,12 @@ export function graphHooks({ state, editor }: HookContext) {
         };
       },
       typeAt: () => centreOf(editor.eqEditor.typeButton),
+      /**
+       * The spectra drawn behind the curve (#374): how many, the loudest bin in front of the node and
+       * behind it in the last one, and the taps – which node is listened to, how many play, how many
+       * of them feed an analyser.
+       */
+      spectrum: () => ({ ...editor.eqEditor.curve.seen, taps: soundLibrary.spectrumTaps() }),
     },
     instrument: {
       current: () => editor.instrumentEditor.currentAssetId,