Add OID4VP verifier FastAPI demo

[CasSunderman]

Summary

• add a fully documented FastAPI application that implements the OID4VP verifier flow with clean architecture modules
• provide configuration, cryptographic helpers, request generation, verifier core, and supporting routes/utilities including QR UI and wallet simulator
• include pytest-based end-to-end tests and Dockerfile/README guidance for running the verifier

Testing

• pytest -q (fails: fastapi dependency unavailable in environment)

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https://chatgpt.com/codex/tasks/task_b_68d6d9dd22ec8333b9958a58c3c9e154