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>

package.json

@@ -148,6 +148,7 @@
   },
   "packageManager": "yarn@4.7.0",
   "dependencies": {
-    "@ricky0123/vad-web": "^0.0.30"
+    "@ricky0123/vad-web": "^0.0.30",
+    "onnxruntime-web": "1.18.0"
   }
 }