mesh-tool: mesht - create/inspect/edit OBJ+STL with ASCII multi-view rendering

- OBJ read/write (multi-object, ngon fan-triangulation, negative indices),
  STL binary+ascii with auto-detect and vertex welding
- info: bbox/size/area/volume + watertightness via edge manifold stats
- view: z-buffered orthographic ASCII renders (front/side/top/iso/back)
- transform: center/mirror/scale/rotate/translate/fit, per-object filter,
  winding auto-flip on negative determinant
- create: box/sphere/cylinder/cone/plane/torus; merge; convert
- go tests: primitive volumes vs analytic values, roundtrips, topology

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MmdG9GqfSWCzts7AkDwRDh

mesh-tool/mesh/transform.go

@@ -0,0 +1,20 @@
+package mesh
+
+// Apply transforms every vertex by mat. Mirroring transforms (negative
+// determinant) flip triangle winding, so it is corrected here to keep
+// normals pointing the same way relative to the surface.
+func (m *Mesh) Apply(mat Mat4) {
+	for i := range m.Verts {
+		m.Verts[i] = mat.Apply(m.Verts[i])
+	}
+	if mat.Det3() < 0 {
+		m.FlipWinding()
+	}
+}
+
+// ApplyAll transforms a set of meshes.
+func ApplyAll(meshes []*Mesh, mat Mat4) {
+	for _, m := range meshes {
+		m.Apply(mat)
+	}
+}