feat(voice): add ONNX WASM idle preloader for Silero VAD

Configures vite-plugin-static-copy to serve @ricky0123/vad-web's ONNX model,
audio worklet, and onnxruntime-web WASM files from the site root.
useOnnxPreloader warms the model cache during page idle so the first mic
click is instant.

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

frontend/vite.config.ts

@@ -1,9 +1,39 @@
 import { defineConfig } from "vite";
 import vue from "@vitejs/plugin-vue";
+import { viteStaticCopy } from "vite-plugin-static-copy";
 import { resolve } from "path";
 
 export default defineConfig({
-  plugins: [vue()],
+  plugins: [
+    vue(),
+    // @ricky0123/vad-web ships ONNX + audio-worklet assets and depends on
+    // onnxruntime-web's WASM binaries. Copy them into the served root so
+    // MicVAD can load them at runtime via `baseAssetPath: "/"`.
+    viteStaticCopy({
+      targets: [
+        {
+          src: "node_modules/@ricky0123/vad-web/dist/*.onnx",
+          dest: "",
+          rename: { stripBase: true },
+        },
+        {
+          src: "node_modules/@ricky0123/vad-web/dist/vad.worklet.bundle.min.js",
+          dest: "",
+          rename: { stripBase: true },
+        },
+        {
+          src: "node_modules/onnxruntime-web/dist/*.wasm",
+          dest: "",
+          rename: { stripBase: true },
+        },
+        {
+          src: "node_modules/onnxruntime-web/dist/*.mjs",
+          dest: "",
+          rename: { stripBase: true },
+        },
+      ],
+    }),
+  ],
   resolve: {
     alias: {
       "@": resolve(__dirname, "src"),