feat: preserve modeling intent across sketches, assemblies, and fabrication

Persist typed sketch dimensions and bounded ordered configuration rules in format 8. Use exact occurrence paths and source identity for editing, movement, appearance, and mass. Preserve sheet material regions through cutting, folding, and exact DXF export; retain nested cavities and material islands.

Validation: cargo xtask ci passed, including 368 engine tests, 178 UI tests, 68 UI scenarios, 136 kernel tests, and the 10-crate wasm check. Actual preview workflows and legacy format-7 origin-corner reopening were inspected.

crates/kernel/src/lib.rs

@@ -64,6 +64,7 @@ pub use offset::with_same_surface;
 pub use ops::{BoolOp, boolean, can_join_touching_faces, split_by_plane, transform, transform_matrix};
 pub use polybool::{faceted_boolean, planar_boolean};
 pub use polyhedron::{HalfSpace, convex_polyhedron, draft, offset_faces, shell};
+pub use prism::{extrude_planar_regions, planar_regions_boolean};
 pub use sew::{EdgeSpec, FaceSpec, SurfSpec, sew};
 pub use splitface::{SplitTool, split_body, split_faces, split_faces_with_map};
 pub use step::step_export;