Probe Connection

Runs a live connectivity probe against the connection's QuickBooks Desktop. This is a real round-trip, not a status read: it enqueues a lightweight company query and waits briefly for the QuickBooks Web Connector to execute it. A `responding: true` result means QuickBooks Desktop is running, the Web Connector is polling, and the bound company file is open right now. If the connector does not answer within the probe window, `responding` is false — QuickBooks is not currently reachable.