Add audit log of MCP tools syncs

- Motivation:
Provide traceability for tools refresh operations (what ran, when, outcome) for debugging and governance.

- Proposed solution:
Persist an audit record during `MCPToolsManager.refresh_mcp_tools` in `backend/aci/control_plane/services/mcp_tools/mcp_tools_manager.py`, expose a read endpoint in `backend/aci/control_plane/routes/mcp_servers.py`, and render a timeline in the MCP server detail view.

- Additional context:
- DB models: `backend/aci/common/db/sql_models.py`
- Frontend: `frontend/src/app/(dashboard)/mcp-servers/[id]/page.tsx` to display logs.