Add onboarding

[staab]

This should probably be done as a separate micro-app, or maybe as a library that can be embedded. Nosta.me is a great start, but their seed words thing is silly. Export ncryptsec only, and get the user set up with a remote signer that they can be confident they can use.

• Splash screen
• Welcome screen
• Profile: name, about, website
• Profile picture with integrated upload or link input
• Explain keys, force user to encrypt and export nsec
• Wizard for signer
  • Checkboxes for platforms they'll be using nostr on
  • If Android, recommend Amber
  • If desktop web, recommend a good extension (nostr connect? keys.band?)
  • If other desktop, recommend a desktop signer (gossip?)
  • If anything else, show a list of remote signers: nsec.app, anything else that exists by then
  • Guides for each recommended signer
• Optional steps:
  • Receive bitcoin
  • Find people to follow
  • Customize relay selections
  • Explore nostr apps
  • Redirect to referrer
  • Set up a nostr address