feat: wire traffic resistance, implement v2 CLI commands, add auth expiry detection
Server:
- Wire traffic resistance decoy generator into main.rs startup behind
--traffic-resistance flag + --decoy-interval-ms config (feature-gated)
Client:
- Implement v2 CLI one-shot commands: send, recv, dm, group create, group invite
All previously printed "coming soon" — now fully functional with MLS state
restoration, peer resolution, KeyPackage fetch, and MLS encryption pipeline
SDK:
- Add SdkError::SessionExpired variant + is_auth_expired() helper for
detecting expired session tokens (RpcStatus::Unauthorized)
- Add ClientEvent::AuthExpired for UI-layer session expiry notification