onHandshakeComplete
Synchronously cancels the transport-aware handshake watchdog the moment Stage 2 completes (NODE_INFO_NONCE received). Does NOT replicate onNodeDbReady's post-NodeDB side effects (analytics, MQTT start, history replay, telemetry requests) — those remain gated on onNodeDbReady at the end of the async DB install block.
See MeshConnectionManager.onHandshakeComplete for the full rationale.