Feature Request: Create Multisig Descriptor from Specter DIY

The main premise of hw wallets is that you can't trust an online computer. When creating a multisig wallet, most users create the multisig-descriptor on their computer, and then verify a Receive address on some of their multisig wallets.

Not verifying the Receive address on *all* of your hw wallets means a compromised computer can give you a QR code with a hacker's xpubs. This can be very confusing for inexperienced users.

My suggestion is to build a flow where users can select seeds that were already loaded to Specter DIY, then load external Zpubs (from QR codes or files), and build the descriptor on the Specter DIY itself.

Then you could export it as a file or QR code. Maybe even as a pdf file with recovery instructions.

The issue names no files or tests; start by examining how Specter DIY loads existing seeds and imports external Zpubs from QR codes or files. Done means users can build a multisig descriptor on the device from those inputs and export it as a file or QR code; a PDF with recovery instructions is only suggested.

Written by the indexing model from the issue text.