IGES 5.3 import and export; OBJ import; STL reading hardened

- IGES import (kernel iges_in, from the published specification). The file
  is restated as STEP and read by the STEP reader, so an IGES file becomes
  the same Import base feature.
  - Manifold solid B-reps (186/514/510/508/504/502).
  - Trimmed (144), bounded (143) and bare B-spline surfaces, sewn into a
    solid by shared edges, with face orientation made consistent.
  - Curves: lines, arcs, ellipses, composite and rational B-spline curves.
  - Surfaces: planes, analytic surfaces 190-198, B-spline surfaces,
    surfaces of revolution and tabulated cylinders.
  - Transformations, units, colours, names (406 form 15 or labels).
  Open, insert and drop .igs/.iges like STEP.
- IGES export (kernel iges_out): each body as a manifold solid B-rep on the
  surfaces a STEP export uses, with name properties and colours.
  ExportCommand to .igs.
- OBJ import as mesh bodies: objects/groups, polygons fanned, negative
  indices, bad lines reported.
- STL: binary files whose header starts with "solid" and those with a zero
  triangle count read as binary; non-finite vertices dropped; facet
  normals ignored; ASCII with non-UTF-8 names. Mesh bodies get consistent
  winding (stray inverted facets turned over).
- Tests: primitives and features round-trip through IGES (volume, area,
  name, colour). Six trimmed patches sew into a closed box. Hostile IGES,
  OBJ and STL inputs never panic. STL quirks. The engine exports a design
  to IGES and opens it again. All 76 oracle parts round-trip through IGES
  with matching volume (local check).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01AS5Tn3xieewUSg3uxrMVdL

apps/solvecraft/src/main.rs

@@ -47,9 +47,13 @@ fn services() -> Services {
     Services {
         pick_open: Some(Box::new(|| {
             rfd::FileDialog::new()
-                .add_filter("Designs, STEP and meshes", &["solvecraft", "step", "stp", "STEP", "STP", "3mf", "3MF", "stl", "STL"])
+                .add_filter(
+                    "Designs, STEP, IGES and meshes",
+                    &["solvecraft", "step", "stp", "STEP", "STP", "igs", "iges", "IGS", "IGES", "3mf", "3MF", "stl", "STL"],
+                )
                 .add_filter("SolveCraft design", &["solvecraft"])
                 .add_filter("STEP", &["step", "stp", "STEP", "STP"])
+                .add_filter("IGES", &["igs", "iges", "IGS", "IGES"])
                 .add_filter("Mesh (3MF, STL)", &["3mf", "3MF", "stl", "STL"])
                 .add_filter("All files", &["*"])
                 .pick_file()