fix: downgrade onnxruntime-web to 1.18 for non-threaded SIMD WASM

ort 1.19+ dropped non-threaded WASM binaries and replaced them with a
threaded .mjs loader that Vite's dev server fails to serve correctly
(wrong MIME type / transform interception). ort 1.18 ships ort-wasm-simd.wasm
which works with numThreads=1 and needs no .mjs dynamic import.

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

vite.config.ts

@@ -50,10 +50,6 @@ 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(),