Import glTF 2.0 files (.glb, .gltf) as mesh bodies (#1512)

glTF files open, insert and drop like 3MF/STL/OBJ: a component named after the file, the node tree as nested rigid components, repeated meshes as occurrences, metres to mm, Y up turned to Z up by default (up: z keeps axes), materials as PBR appearances. Bounded, hostile-input tested reader; no new persisted data. Closes #1505.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

crates/engine/src/tests.rs

@@ -307,6 +307,7 @@ mod blend_fit;
 mod boolean_diagnostics;
 mod component_frames;
 mod curved_seam_round;
+mod gltf_import;
 mod import_component;
 mod large_step_import;
 mod loft_cut;