Merge ActionAddPart into ActionClone by adding a Drawing constructor,
eliminating the redundant class. ActionClone now handles both adding
new parts from a drawing and cloning selected part groups. Added
Ctrl+F fill support for groups using FillLinear pattern tiling, and
adopted quadrant-aware push directions from ActionAddPart. Refactored
FillLinear to extract shared helpers and add a Fill(Pattern) overload
for tiling arbitrary part groups across the work area.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
