Address claude-review round 7 nits on #919:
- Add test_validate_via_userinfo_rejects_non_http_scheme — a non-http(s)
userinfo_uri is refused before any request (covers the SSRF scheme guard).
- Docstring caution on _validate_via_userinfo: userinfo-validated tokens carry
empty scopes, so management endpoints must not gate on scopes for this path.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>