Add Smoothing to the Freehand Tool

Freehand tool: "smoothing" checkbox in its control bar, which adds a smoothing node downstream of the Path node.

Start by locating the Freehand tool's control bar and the Path node implementation. Trace how tool options create downstream nodes, then add the smoothing checkbox behavior so enabling it inserts a smoothing node after Path. Done means the control is available and the resulting node chain matches the requested behavior.

Written by the indexing model from the issue text.