Move wrtc to optionalDependencies

wrtc requires native compilation and may fail on some systems.
Make it optional so the demo can build without it. Users who want
to run the Node.js test script can install it separately.

🤖 Generated with Claude Code
https://claude.com/claude-code

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

package.json

@@ -16,7 +16,9 @@
     "qrcode": "^1.5.4",
     "react": "^18.2.0",
     "react-dom": "^18.2.0",
-    "react-hot-toast": "^2.6.0",
+    "react-hot-toast": "^2.6.0"
+  },
+  "optionalDependencies": {
     "wrtc": "^0.4.7"
   },
   "devDependencies": {