feat(core): pitch shift — a granular shifter as the fifth FX worklet

Adds hf-pitchshift alongside the four existing dynamics worklets: a dual-tap
granular delay line, 100 ms grain, taps 180° apart so one is always
crossfading in as the other resets — hides the splice each tap makes on
wrap. Read-tap speed relative to the write head tracks the semitone ratio,
so pitch shifts without changing duration.

Registered through the same workletBuilder/dispose-message path the other
four use (so shapeOf never rebuilds on a param tweak, and a chain drop
retires it), wired into the registry with a plain-language copy entry and a
~0.2s chain tail (two grains). One implementation, shared by preview (Web
Audio in the page) and render (the same worklet run inside an
OfflineAudioContext in the headless browser) — confirmed by a browser-render
test that measures the actual output frequency, not just that it differs
from input.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

packages/core/src/audioFx.ts

@@ -505,6 +505,35 @@ export const HF_AUDIO_FX: readonly HfAudioFxDef[] = [
     ],
     web: "worklet-bitcrush",
   },
+  {
+    id: "pitchshift",
+    label: "Pitch shift",
+    group: "time",
+    description: "Shifts pitch up or down without changing playback speed.",
+    params: [
+      {
+        kind: "number",
+        key: "semitones",
+        label: "Semitones",
+        unit: "st",
+        min: -12,
+        max: 12,
+        step: 1,
+        default: 0,
+      },
+      {
+        kind: "number",
+        key: "mix",
+        label: "Mix",
+        unit: "",
+        min: 0,
+        max: 1,
+        step: 0.01,
+        default: 1,
+      },
+    ],
+    web: "worklet-pitchshift",
+  },
 
   {
     id: "delay",