v0.4.2.0 fix: repair generated OpenSCAD compile failures (#16)

* fix: repair OpenSCAD compile failures after generation

Preserve rejected LLM-generated SCAD, feed real CGAL diagnostics into the repair skill, compile the repaired source before rendering, and retain the latest source for human review when repair still fails.

* fix: preserve repair progress event contracts

* fix: harden compiler-guided CAD repair