Add live demo page

[fregante]

1. Copy setup from https://refined-github.github.io/github-url-detection
2. Make these changes:
   • import URL list from index.test.js and use it create a baseline list of demos
   • use field to add a real-time output (no need to use datalist here)

LLMs welcome, just copy the html/style/parcel setup from that other repo because I already know it works.