Update quarto-hub to samod 0.8+ and re-implement document access audit logging

[shikokuchuo]

This currently depends on our fork of samod, which implements AccessPolicy in line with the js reference, with the expectation that this will be upstreamed.

We always allow access, only log — AuditAccessPolicy::should_allow() always returns true. It's used for audit logging, not authorization. Authorization can be layered on later by returning false for denied peers.

Summary

• Upgrade samod dependency to 0.8+ (3af4595), adopting the new AcceptorHandle, dial_websocket, and AccessPolicy APIs
• Replace the custom peer connection loop with samod's built-in dial_websocket dialer (automatic reconnection with exponential backoff)
• Switch inbound WebSocket handling from the old accept_axum → handshake_complete → finished pattern to the new event-stream pattern (AcceptorEvent::ClientConnected / ClientDisconnected)
• Implement document access audit logging via samod's upstream AccessPolicy trait, replacing the previous ConnectionId-based approach with a PeerId-based one