Todo 32: Session UI

Status

done

Goal

Expose persisted sessions in the debug console so users can create/load sessions, replay chat messages and audit logs, and inspect call/turn/session usage.

Scope

Add sidebar session controls for creating, refreshing, selecting, and loading sessions.
Send the selected session_id in the first WebSocket request while preserving lightweight follow-up turn messages.
Handle session_started.session_id from the backend.
Add a separate audit replay panel.
Add session usage displays for aggregate, turn, and model-call usage.
Keep live round stats separate from session aggregate usage.

Verification

Static UI tests cover session controls, replay panels, session API calls, session_id WebSocket payloads, and usage render hooks.
WebSocket tests still prove multi-turn reuse behavior.
node --check src/agent_lab/presentation/static/app.js passes.
uv run pytest tests/test_websocket_api.py -q passes: 34 tests.
uv run pytest passes: 66 tests.