Adds a click-to-measure area mode triggered by Ctrl+Shift+A. Each LMB
click expands the picked triangle into its connected coplanar patch
(BFS over shared edges, dot(normal, seed) > 0.9999); re-clicking
removes that patch; Alt+LMB skips expansion for a single triangle.
Picks across different meshes accumulate as separate patches.
ViewportWindow gains pickMeshLocalAt (screen pick → mesh-local hit
via inverse composed transform) and a tool-mode pattern mirroring
the section tool (toggleAreaTool, surfacePickedInTool signal,
areaToolToggled signal, Esc to exit). Per-mesh adjacency is built
lazily on first pick of each mesh and dropped on tool toggle.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
Adds neutral primitives on ViewportWindow (readbackMeshTriangles,
findInstance) so consumers can compute per-object geometry queries
without the library retaining a CPU triangle copy. Measurement.cpp in
ifcviewer-full uses them to sum signed-tetrahedra in mesh-local space,
weighted by |det(placement_3x3)| per instance for mapped-item scaling.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
Dion Moult