Shape List hierarchy phase 1: organizational groups and outliner

[trailcode]

Summary

• Organizational Shape List hierarchy: groups, current group, DnD reparent (including drop-to-root), Group / New group / Ungroup, cascade delete, Ctrl multi-select.
• Boolean/extrude parenting rules; Hide all preserves per-shape visibility.
• STEP XCAF assembly import as a group tree (optional Union shapes); Import dialog UX on this branch.
• Docs, CHANGELOG, and shp_tests coverage.

Closes #217

Related

• Shape List hierarchy phase 1: organizational groups and outliner #217 documents this work (phase 1)
• Shape List hierarchy phase 2: reorder, duplicate group, selection polish #215 phase 2 / Shape List hierarchy phase 3: parent transforms and advanced assembly model #214 phase 3 follow-ups
• Compound / assembly modeling in EzyCad #59 compound / assembly modeling

Test plan

• Shape List: create/nest groups, empty group as current, add box under it
• DnD onto group name, onto child solid, onto empty pad (root)
• Ungroup moves all direct children; cascade delete + undo
• Hide all / group visibility
• STEP multi-body import with and without Union shapes
• EzyCad_tests.exe --gtest_filter=Shp_test.*

[cursor]

Bugbot is not enabled for your account, so this pull request was not reviewed.

Enable Bugbot in the Cursor dashboard to get automatic reviews on future PRs.