Onchain reference design revision progress tracker

[GBKS]

This is a tracker issue for a larger chunk of work going on around revising the onchain reference designs in the guide (savings, shared, upgradeable). We discussed this thoroughly in jam sessions and our working doc, so I'm moving this to an issue here for better tracking.

I'll group things by the likely page structure we'll have in the end. For all the details, see the planning document.

Reference designs

• [ ] Savings wallet
• [ ] Shared wallet
• [ ] Upgradeable wallet
  • [ ] #777
• [ ] Wallet management
  • [x] #867
  • [x] #986

How it works

• [ ] Complex spending conditions
  • [x] #992
  • [x] #847
• [ ] Key rotation (via FROST)
• [ ] Musig (may be enough as a glossary entry)

I'll update this issue as we go.