Improve clarity in 'Export room keys'

### Your use case


This screen is confusing users:

- Non legible, people aren't reading walls of text
- Scanning the labels misleads into inputting your old passphrase, when it's asking for a new one
- Easy to confuse with your account password, which, ironically would work on input

### Have you considered any alternatives?

_No response_

### Additional context

Thanks for raising @arthursinclair! Brief internal discussion:

https://matrix.to/#/!ZCWYLfAKXolsPWObuZ:matrix.org/$eRS0ag8vUqCV3uMpD9NZmW-WlWj3JJt_oAF2hjHb-SE?via=matrix.org&via=element.io&via=vector.modular.im