Muggable: QR code modal for every discovered address

[dmnyc]

Every Bitcoin address Muggable discovers should offer a QR code view, so users can move funds without copying the raw string into a wallet.

Proposal

• Add a QR affordance next to each discovered address row.
• Clicking it opens a modal showing:
  • a QR code encoding the address
  • the address itself, with a copy button
  • a one-line caption on where the address came from (derivation/discovery source)
• qrcode.react is already in package.json (^4.2.0), so no new dependency.

Acceptance

• Every discovered address row has a QR affordance.
• Modal closes via X, backdrop click, and Escape.
• Renders correctly in light and dark mode.
• Copy button copies the raw address (not the QR payload wrapper).