Import FreeCAD and Rhino files through cadmpeg (#1435)

FreeCAD .FCStd and Rhino .3dm files open, insert and drop like STEP and IGES:
cadmpeg (Apache-2.0, pinned =0.6.1, native builds only) detects the format,
decodes it under its service resource caps, validates the model and writes it
as STEP AP214, which becomes an Import feature in a new component named after
the file, with the up and names options.

Only the fcstd, rhino and step codecs are compiled in (no default features).
ACIS is left out: cadmpeg's sat codec is a ShapeManager stream decoder.
native_cad.rs is the single importer seam. Self-made FreeCAD and Rhino box
fixtures, hostile-input, ZIP-bomb and cap tests, engine tests for the
component path; the browser build reports these formats as not supported.
A note under design format 23 says an Import's file can name these formats.

Co-authored-by: Jacob Oursland <jacob.oursland@gmail.com>
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

ATTRIBUTION.md

@@ -110,6 +110,8 @@ Editable drawing code, native projects and shipped exports are collected under `
 | assets/shaders/viewport.wgsl | SolidCraft contributors | Original SolidCraft resource data or drawing code, collected without redesign | MIT OR Apache-2.0 |
 | assets/styles/ui/palettes.rs | SolidCraft contributors | Original SolidCraft resource data or drawing code, collected without redesign | MIT OR Apache-2.0 |
 | assets/styles/web/loading.css | SolidCraft contributors | Original SolidCraft resource data or drawing code, collected without redesign | MIT OR Apache-2.0 |
+| crates/io/src/native_cad/fixtures/block.FCStd | SolidCraft contributors | original 10 × 20 × 30 mm test box saved by FreeCAD 1.1.4 run as an external program (`make_block_fcstd.py` beside it); no third-party geometry | MIT OR Apache-2.0 |
+| crates/io/src/native_cad/fixtures/block.3dm | SolidCraft contributors | original 10 × 20 × 30 mm test box written with McNeel's MIT-licensed rhino3dm Python package (`make_block_3dm.py` beside it); no third-party geometry | MIT OR Apache-2.0 |
 
 | docs/book/src/og.png | SolidCraft contributors | copy of assets/branding/web/source/og.png staged by cargo xtask book (gitignored) | MIT OR Apache-2.0 |
 
@@ -151,6 +153,16 @@ in THIRD-PARTY-LICENSES.txt; no images or artwork from that project are copied.
 The glTF test files are built by the tests themselves (crates/io/src/gltf_in_tests.rs,
 crates/engine/src/tests/gltf_import.rs); no third-party models are committed.
 
+## FreeCAD and Rhino import library
+
+FreeCAD `.FCStd` and Rhino `.3dm` files are read with [cadmpeg](https://github.com/cadmpeg/cadmpeg)
+0.6.1 (Apache-2.0), linked as the crates `cadmpeg-core`, `cadmpeg-ir`, `cadmpeg-registry`,
+`cadmpeg-container`, `cadmpeg-codec-freecad`, `cadmpeg-codec-rhino` and `cadmpeg-codec-step`
+in native builds (`crates/io/src/native_cad.rs`). Only those open-format codecs are built: no
+default features, so cadmpeg's codecs for commercial CAD formats and its ShapeManager/ACIS
+codec are not compiled in. Its licence text is in THIRD-PARTY-LICENSES.txt; no code from it is
+copied into SolidCraft.
+
 ## Recovered contributions
 
 | SolidCraft file | Original contribution | Licence |