feat: support nodePubkeys invoice checks

[andrerfneves]

Summary

Implements draft LUD-XX nodePubkeys support for LNURL-pay payRequest responses, aligned with the local proposal in /home/exedev/code/lud-proposals/lud-xx-node-pubkeys.md and the open upstream spec PR: lnurl/luds#297.

I verified the local proposal and PR #297 are byte-identical. The design is also materially stronger than older prior art like lnurl/luds#204 because it keeps the human Lightning Address unchanged and attaches structured invoice-origin metadata to the LUD-06 response.

What changed

• Parse and validate optional payRequest.nodePubkeys:
  • non-empty array
  • object entries with required pubkey
  • compressed secp256k1 public key, 66-char hex, normalized lowercase
  • duplicate rejection
  • forward-compatible raw fields preserved
• Extend BOLT11 validation to return the effective payee node id:
  • uses BOLT11 n tag when present
  • falls back to signature recovery when n is absent
• Add payment.nodePubkeyVerification for BOLT11 instructions:
  • status: "verified" with matched pubkey
  • status: "mismatch" with non-blocking warning by default
• Add nodePubkeyPolicy:
  • "warn" default — spec-compatible non-blocking warning result
  • "enforce" — throws NodePubkeyMismatchError
  • "off" — skips nodePubkeys comparison while preserving other BOLT11 validation
• Export public types/errors:
  • NodePubkey
  • NodePubkeyPolicy
  • NodePubkeyVerification
  • Bolt11PayeeNodeIdSource
  • NodePubkeyMismatchError
• Update README, SECURITY, CHANGELOG, and examples.
• Add a runnable local examples/basic/node-pubkeys.ts using real signed test invoices.

Verification

• bun run check ✅
  • typecheck ✅
  • examples typecheck ✅
  • Biome lint/check ✅
  • unit/integration/e2e tests: 145 pass ✅
  • package smoke tests: 3 pass ✅
• bun examples/basic/node-pubkeys.ts ✅
• npm publish --dry-run ✅

Notes

This intentionally follows the LUD proposal's wallet UX: mismatches are surfaced but not blocked by default. Strict blocking is available only as an explicit caller policy.