fix: suppress replayed load session updates from output

[dutifulbob]

Summary

Fix replay leakage on reconnect/load by suppressing replayed session/update notifications at the ACP forwarding layer.

What changed

• Added AcpClient replay gate: suppressReplaySessionUpdateMessages.
• During loadSessionWithOptions(..., suppressReplayUpdates: true), suppress only inbound JSON-RPC notifications where method === "session/update".
• Kept protocol flow intact (controller.enqueue(...)) and continued forwarding all non-session/update ACP messages.
• Restored suppression state in finally and reset it on client close.
• Extended mock agent to simulate replay-on-load:
  • --replay-load-session-updates
  • --load-replay-text <text>
• Added integration coverage for the reconnect/load path:
  • replayed updates are not emitted in JSON output
  • non-update load request/response still visible
  • replayed updates are not written to session event log
  • live prompt chunk is still emitted and persisted

Why

Adapters may replay historical session/update notifications on session/load. Those were being forwarded raw, causing stale pre-turn output to leak to consumers like OpenClaw.

Validation

• npm run typecheck
• npm run lint
• npm run format:check
• npm run build
• npm test

All passed locally.