Implement optional SAO connection (REST + WebSocket)

[jbcupps]

Description

Add SAO connectivity to Abigail so it can register with and submit evaluations to the orchestrator, while maintaining standalone capability.

Acceptance Criteria

• Abigail connects to SAO via REST + WebSocket when configured
• Registration sends Ed25519 public key to SAO
• All requests signed with Ed25519 (X-Agent-Id, X-Agent-Signature, X-Agent-Timestamp)
• Abigail works fully standalone when SAO is unavailable
• Connection status visible in UI
• Graceful reconnection on disconnect

Timeline

Phase 2: Weeks 4-5 (target: 2026-04-01)

References

• INTEGRATION_GUIDE.md
• Project board: AI_Ecosystem