Add Node on Edge Drop

Demonstrates the enriched OnConnectEnd callback. Its BlowConnectEndInfo payload carries the originating handle, the drop position in flow coordinates, whether the drop landed on a valid handle, and whether the gesture really was a drop (IsDropped) of a new connection rather than a reconnect (IsReconnect). Drag a connection into empty space to spawn a new, already-connected node where you released - downstream from a source handle, upstream from a target handle; drop on a handle to connect normally.