Shape a sound with a Parametric EQ and its own curve editor (#367)

A sound FX or an instrument had a 5-Band-EQ with fixed bands and a
Filter with one band. The Parametric EQ holds up to ten bands of any
type, and a double-click on the node opens an editor that draws the
curve they make together.

- The bands are a list on the node (`bands`): type, frequency, gain,
  Q and slope. A hand-edited project is held to the editor's ranges
  and to ten bands.
- Each band compiles to the existing `pass` stage, so the audio core
  is unchanged. A peak or a shelf at 0 dB is left out.
- The curve is worked out in `parametricEq.ts` with the biquad
  formulas of the Web Audio spec, so the editor draws what is heard.
- The editor is a window that floats over the editor without a
  backdrop, so the tab's Play stays usable. A double-click adds a
  peak, a drag moves a band, the wheel turns its Q, a right-click
  removes it. Fields below the curve set the picked band. It opens in
  the middle of the screen and moves by its title bar.
- A drag or a scrub writes the node as a preview and makes one undo
  step on release. The panels hear of the preview once a frame, and
  the window lays itself out only when one of its texts changes.
- The area under the curve is filled as one shape for each side of
  0 dB. As a single shape it crossed itself and came apart.
- The curve works out each band's coefficients once and adds the sum
  up from the bands. A drag took 295 ms of script time in a profile
  before and 64 ms after.

Decided on my own:
- Bands are added by a double-click, so a single click can let go of
  the picked band without adding one.
- The cuts are labelled "Low cut" and "High cut" as in an EQ, not
  "High-pass" and "Low-pass" as on the Filter.
- The bands have no input, so no parameter or Envelope moves them.

Tests:
- Unit parametric-eq (new) and soundfx: 69 green. Counter-probe with
  no stages emitted: the compile test red. Counter-probe with one
  fill shape: the fill test red.
- e2e 34 (melektaus-atx): ALL PASSED, 96 checks (3 new).
- Counter-probe e2e: no stages emitted, the playing check red.
- Gate (melektaus-atx): CHECK EXIT 0, 274 files, 4230 tests.

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

src/editor/debug/graphHooks.ts

@@ -1,5 +1,6 @@
 import { NameTransitionCommand } from '../../core/commands/graphCommands';
 import { currentNodePalette } from '../graph/NodePalette';
+import { currentEqEditor } from '../soundfx/EqEditor';
 import { rectOf } from '../textProbe';
 import { centreOf, snapButton, type HookContext } from './hookHelpers';
 
@@ -114,6 +115,35 @@ export function graphHooks({ state, editor }: HookContext) {
       /** 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),
+      nodeAt: (nodeId: string) => editor.soundFxEditor.canvas.nodeGlobal(nodeId),
+    },
+    /** The Parametric EQ's window (#367): for which node it is open, its bands and where to aim. */
+    eq: {
+      shown: () => currentEqEditor()?.shownFor ?? null,
+      bands: () => currentEqEditor()?.bands() ?? null,
+      picked: () => currentEqEditor()?.picked ?? null,
+      handleAt: (index: number) => currentEqEditor()?.curve.handleGlobal(index) ?? null,
+      pointAt: (hz: number, db: number) => currentEqEditor()?.curve.pointGlobal(hz, db) ?? null,
+      fields: () => {
+        const eq = currentEqEditor();
+        return (
+          eq && {
+            type: eq.typeButton.text,
+            slope: eq.slopeButton.enabled ? eq.slopeButton.text : null,
+            gain: eq.gainField.enabled ? eq.gainField.value : null,
+            q: eq.qField.enabled ? eq.qField.value : null,
+            frequency: eq.frequencyField.value,
+          }
+        );
+      },
+      typeAt: () => {
+        const eq = currentEqEditor();
+        return eq ? centreOf(eq.typeButton) : null;
+      },
+      closeAt: () => {
+        const eq = currentEqEditor();
+        return eq ? centreOf(eq.closeButton) : null;
+      },
     },
     instrument: {
       current: () => editor.instrumentEditor.currentAssetId,