[FR] Local Backup

### Description

Local backups of everything is needed in case you need to reinstall or if you are transferring over to a new device. Not everyone uses clouds & syncs so it would be great if there were multiple local backup methods.

A way to save a pages individually as text, markdown, or pdf. A zip export for doing multiple pages at once including sub-pages within a page. A restore method for when reinstalling on a new or same device the workspace including all pages perhaps a .json?

### Impact

It would really be benefitical for everyone especially those who build books on phones.

### Additional Context

_No response_