feat: some chat UX improvement ideas

[SgtPooki]

• it would be cool if last X-time/count chat history was stored

• would be cool to run js side in service-worker/web-worker so we could get messages while offline (until browser kills it anyway)

• emoji icon is currently broken in brave + firefox (I assumed clicking would allow me to choose an emoji, but I get no response or visual feedback)

[2color]

I've removed the emoji button for now.

There's no (w3c/editing#350) standard way of loading the OS emoji keyboard. That means that implementing this would require a custom emoji picker which I'd like to avoid.