refactor: migrate to domain-oriented package structure
test(coverage): make reports subprocess-aware
test(gui): exercise full MainWindow workflow
test(suite): add portable regression and tox suites
fix(cli): avoid Qt logger shutdown error in quiet export
test(core): cover GIR handling for U-shaped contours
fix(core): prevent offset collapse from degenerate spline ends
refactor(core): unify lead-in straight length across compensation modes