feat(stellar): add send QR scanner

[Hallab7]

QR code scanner for send flow

Summary

• add raw meta-address and stellar: URI QR variants to the Stellar receive flow
• add a mobile-friendly camera scanner to the Stellar send form
• populate recipient, amount, and memo fields from supported QR payloads
• show a file-picker fallback when camera permission is denied or unavailable
• decode selected QR images entirely in the browser without uploading them
• add shared QR parsing, URI generation, permission classification, and image-decoding utilities

Testing

• pnpm exec vitest run src/utils/qr.test.ts
• pnpm exec tsc --noEmit
• pnpm run build
• git diff --check

Acceptance criteria

• Receive view offers QR codes for the raw meta-address and Stellar URI
• Send view scans with the device camera and fills the recipient
• Raw meta-addresses and Stellar URIs are accepted
• Camera denial or unavailability displays the image fallback
• Receive-generated Stellar URIs round-trip through the send parser
• Selected images are decoded locally and never uploaded

closes #108

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[truthixify]

Rebase against develop. The Vercel check will still fail (infra), but conflicts need clearing first.