Trigger the submit button in the note composer.

It's a pet-peeve of mine, and very minor. But due to my visual impairment, I use a magnifier, at 400%, so submitting means mousing around, which in turn means shifting my entire viewpoint around - which is quite annoying x)

Many services, like Github, have ctrl+enter to send/submit. So far, basically no Nostr client does this. And it _bothers_ me. xD