Add QR code support so users can share wallet addresses and scan payment codes for quick transfers.

[memplethee-lab]

Issue Description

Add QR code support so users can share wallet addresses and scan payment codes for quick transfers.

Problem

Users currently have no convenient way to exchange wallet addresses or initiate a payment quickly from a mobile device.

Scope

• Add QR code generation for a wallet address or receive flow.
• Add QR scanning support to populate recipient or payment details.
• Ensure the feature works reliably in a mobile-friendly interface.

Acceptance Criteria

• Users can generate a QR code for their wallet address.
• A scanned QR code can populate the payment form or recipient field.
• The experience is reliable and understandable for first-time users.
• The feature degrades gracefully when camera access is unavailable.

Suggested Implementation Notes

• Keep the first version focused on core payment sharing and scanning.
• Handle permissions and fallback states clearly.
• Avoid adding unnecessary complexity to the initial workflow.