fix: copy ort .mjs file, add COOP/COEP headers, set numThreads=1

The threaded ORT WASM requires ort-wasm-simd-threaded.mjs to be served
alongside the .wasm files, and needs SharedArrayBuffer (COOP/COEP headers).
Add the .mjs to the static copy targets, add the required headers to the
Vite dev server, and set ort.env.wasm.numThreads=1 as a single-threaded
fallback that avoids the SharedArrayBuffer requirement entirely.

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

vite.config.ts

@@ -50,6 +50,10 @@ export default ({
           src: "node_modules/onnxruntime-web/dist/*.wasm",
           dest: "vad",
         },
+        {
+          src: "node_modules/onnxruntime-web/dist/ort-wasm-simd-threaded.mjs",
+          dest: "vad",
+        },
       ],
     }),
     react(),
@@ -118,6 +122,11 @@ export default ({
         key: fs.readFileSync("./backend/dev_tls_m.localhost.key"),
         cert: fs.readFileSync("./backend/dev_tls_m.localhost.crt"),
       },
+      // Required for SharedArrayBuffer (used by onnxruntime-web threaded WASM)
+      headers: {
+        "Cross-Origin-Opener-Policy": "same-origin",
+        "Cross-Origin-Embedder-Policy": "require-corp",
+      },
     },
     worker: {
       format: "es",