test: add JWT signature verification tests to catch crypto issues

[felippemsc]

Summary

• Add 3 tests that exercise jsonwebtoken::decode() end-to-end with real EC key pairs
• These tests would have caught the jsonwebtoken 9→10 CryptoProvider panic (chore(deps): bump jsonwebtoken from 9.3.1 to 10.3.0 #23)
• Uses a hardcoded P-256 test key pair — no network or external dependencies needed
• Also includes the rust_crypto feature fix for jsonwebtoken 10

New tests

• verify_signature_with_valid_jwt — sign + verify round-trip
• verify_signature_rejects_wrong_key — wrong JWKS key fails verification
• verify_signature_rejects_missing_kid — missing key ID returns KeyNotFound error

Test plan

• All 25 tests pass (cargo test)