Address round-1 claude-review nits on PR #894:
- Document why offline_access is advertised unconditionally (independent of
settings.enable_offline_access): per RFC 8414, scopes_supported lists what
the AS *can* support, with actual issuance still gated upstream by Nextcloud.
- Add a regression test proving the offline_access invariant holds on an empty
FastMCP instance with no registered tools.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>