feat: add Silero VAD toggle to audio pipeline

Integrates @ricky0123/vad-web's MicVAD as an optional voice activity detector
alongside the noise gate. When enabled, the Silero ONNX model classifies each
audio frame as speech or silence; silence frames mute the worklet's output via
a new VAD gate message. VAD is wired into Publisher.ts alongside the existing
noise gate transformer. Vite is configured to copy the worklet bundle, ONNX
model, and ORT WASM files to /vad/ so they're reachable at runtime.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

vite.config.ts

@@ -14,6 +14,7 @@ import {
 } from "vite";
 import svgrPlugin from "vite-plugin-svgr";
 import { createHtmlPlugin } from "vite-plugin-html";
+import { viteStaticCopy } from "vite-plugin-static-copy";
 
 import { codecovVitePlugin } from "@codecov/vite-plugin";
 import { sentryVitePlugin } from "@sentry/vite-plugin";
@@ -35,6 +36,22 @@ export default ({
   // build time.
   process.env.VITE_PACKAGE = packageType ?? "full";
   const plugins: PluginOption[] = [
+    viteStaticCopy({
+      targets: [
+        {
+          src: "node_modules/@ricky0123/vad-web/dist/vad.worklet.bundle.min.js",
+          dest: "vad",
+        },
+        {
+          src: "node_modules/@ricky0123/vad-web/dist/silero_vad_legacy.onnx",
+          dest: "vad",
+        },
+        {
+          src: "node_modules/onnxruntime-web/dist/*.wasm",
+          dest: "vad",
+        },
+      ],
+    }),
     react(),
     svgrPlugin({
       svgrOptions: {