use @sctlib/rtc to sync yjs document between webRTCPeer(s)

• refactor yjs addition, so the URL hash param #data= is send from yjs document changes -> also renders QR and textare
• add yjs with @sctlib/rtc support, so two peers can connect together and edit a document

Docs:

• https://docs.yjs.dev/api/document-updates#update-api
• https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint8Array
• https://developer.mozilla.org/en-US/docs/Web/API/RTCDataChannel/send