[Mobile] Wallet: integrate Breez SDK Liquid (React Native) + NWC

[Salmatcre8]

Summary

Bring the Lightning wallet to the mobile app. Good news: Breez ships a React Native SDK, so we
replace the in-browser WASM (@breeztech/breez-sdk-liquid) with the native binding instead of
fighting WASM on mobile. This should be more reliable than web.

Target / reference

• Web adapter to mirror: src/lib/wallet/breezAdapter.ts (and the NwcAdapter + shared store
  interface). Keep the same adapter shape on mobile so screens stay portable.
• Native package: @breeztech/react-native-breez-sdk-liquid — verify the exact package name and
  current version when starting; Breez naming has changed over releases.

Tasks

• Add the Breez React Native SDK; this requires a dev build (EAS), not Expo Go.
• Initialize the SDK with NEXT_PUBLIC_BREEZ_API_KEY's mobile equivalent (config, not a secret —
  Breez ships it client-side by design).
• Feed it the mnemonic produced by the key-derivation spike (blocked on that issue).
• Implement: show balance, receive (BOLT11 invoice + QR), send (pay invoice) — matching web.
• Also port the bring-your-own NWC path (@getalby/sdk) so users with Alby/Mutiny/Primal
  can connect, same as web.

Acceptance criteria

• On a dev build, a wallet initializes from the derived mnemonic, shows a real balance, and can
  generate a receive invoice and pay one on Liquid/Lightning.
• NWC connect works for at least one external wallet.

Blocked by

• Key-derivation spike (the wallet needs a mnemonic/seed source first).