Skel: Slice A — Bone CRUD (create / remove / rename / duplicate)

[fernandotonon]

Parent epic: #554

Goal

Direct bone-level CRUD on the skeleton of a selected entity: create a new bone (under a chosen parent), remove a bone (with optional weight transfer to parent), rename, duplicate. The user-requested foundation that every other slice depends on.

Scope

• New singleton SkeletonEditor (src/SkeletonEditor.{h,cpp}) — main-thread, getSingleton/kill, signals boneCreated(name), boneRemoved(name), boneRenamed(old,new).
• Create bone:
  • Pick parent bone in the inspector or right-click on a bone in the viewport.
  • Default placement: at parent's tail, oriented along parent's axis. User can drag with TransformOperator immediately after creation.
  • Auto-name: Bone, Bone.001, Bone.002 (Blender convention).
• Remove bone:
  • Confirmation prompt if the bone has children (offer "remove with children" vs "promote children to parent").
  • Weight transfer: any vertex weighted to the removed bone gets its weight reassigned to the parent (renormalized). Toggle for "transfer to parent" vs "drop weight".
  • Refresh every SubMesh::getBoneAssignments referencing the removed handle.
• Rename bone: inline edit in the outliner or context menu. Must propagate to:
  • Every animation track in every clip that references the bone (AnimationMerger-style renaming).
  • Every VertexBoneAssignment (handle stays the same; only the name field changes — Ogre stores by handle).
  • The QML inspector / weight overlay caches.
• Duplicate bone: clones name (with .001 suffix), TRS, parent. Does not clone children (different operation; covered in Slice B's "split chain").
• Undo: new commands CreateBoneCommand, RemoveBoneCommand, RenameBoneCommand, DuplicateBoneCommand. Each rebuilds the affected vertex assignments + animation tracks atomically.
• Ogre quirk: there's no Skeleton::removeBone. Bone deletion walks the bone list, rebuilds handles via Skeleton::_buildMapBoneByHandle, then rewrites every SubMesh::clearBoneAssignments / addBoneAssignment referencing the moved handles. Treat as the most complex op in this slice.

Acceptance Criteria

• Create-bone-from-parent produces a bone visible in the outliner and SkeletonDebug overlay; drag with the gizmo works.
• Remove-bone with "transfer to parent" leaves the mesh deforming correctly with the parent absorbing the removed bone's influence.
• Rename-bone propagates to every animation clip and the bone shows up under the new name in dope sheet / curve editor.
• Duplicate-bone creates a sibling with .001 suffix.
• Every operation is undoable end-to-end (including weight transfers and clip renames).
• No regression in BoneDragRelease's drag-with-auto-key path.
• Sentry breadcrumbs scene.skel.bone.create, .remove, .rename, .duplicate.
• Headless-CI tests cover each op on a 2-bone fixture skeleton.

Effort

~9 days. Bone removal's handle-rebuild is the schedule risk.