[WALLET-46] Export ProofCredentialV1 and verify aud

[frostevent]

Summary

• Export the ProofCredentialV1 class from the Node entry (src/index.node.ts) so callers can narrow a ProofCredential via instanceof ProofCredentialV1 and use its accessors (givenName(), dateOfBirth(), isOver18(), etc.). ProofCredential is already re-exported via export type * from "./types.ts". Kept off the browser entry since verify/verifyVPToken are Node-only.
• Add an optional aud parameter to verify and verifyVPToken. When supplied:
  • With a KB JWT present, it asserts kbJwt.payload.aud === aud and throws on mismatch.
  • With no KB JWT present, it throws — consistent with how a present KB JWT already requires a nonce.
  • aud is threaded through verifyVPToken → verify.

Testing

• yarn check-all passes (format, lint, typecheck, publint).
• Browser-graph grep after yarn build is clean (no @sd-jwt/@owf/node: leaks).
• This repo has no automated test suite; the quality gate is yarn check-all.

Jira: https://notarize.atlassian.net/browse/WALLET-46

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