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>

package.json

@@ -132,6 +132,7 @@
     "vite-plugin-generate-file": "^0.3.0",
     "vite-plugin-html": "^3.2.2",
     "vite-plugin-node-stdlib-browser": "^0.2.1",
+    "vite-plugin-static-copy": "^4.0.0",
     "vite-plugin-svgr": "^4.0.0",
     "vitest": "^4.0.18",
     "vitest-axe": "^1.0.0-pre.3"
@@ -145,5 +146,8 @@
     "qs": "^6.14.1",
     "js-yaml": "^4.1.1"
   },
-  "packageManager": "yarn@4.7.0"
+  "packageManager": "yarn@4.7.0",
+  "dependencies": {
+    "@ricky0123/vad-web": "^0.0.30"
+  }
 }