hotkey to end 'adding parts'

possibly 'esc' (whilst no polygon is being drawn)

Alternatively in the dialog box where you are entering a part name, add a button for 'done ' / 'done (all parts)' .

No files or tests are named. Start by locating the code for polygon drawing, the part-entry dialog, and existing keyboard handling; implement a way to finish adding parts with Escape when no polygon is being drawn or with a dialog button, then verify that the selected action ends part entry without interrupting polygon drawing.

Written by the indexing model from the issue text.