feat: Convert to Sheet Metal takes a solid or a shelled body by its bend edges (#725)

Convert to Sheet Metal now takes a solid or a shelled body by its bend edges (`bends`): the faces reached from the fixed face across those edges become the sheet, keeping the part's envelope, with the flat pattern by the rule's K-factor and radius. Other edges between sheet faces are cut open. The result works with edge flanges, cuts, Unfold/Refold, the flat pattern and DXF. A conversion without `bends` is the plate conversion as before. The optional `bends` field is noted under format 17. Fixes #647.

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

crates/doc/src/sheet.rs

@@ -16,6 +16,10 @@ use solidcraft_kernel::{self as kernel, Body, EdgeSpec, FaceSpec, SurfSpec};
 use crate::expr::{self, Kind, Value};
 use crate::{DocError, Document, IDENTITY, Mat, Result, apply_point, apply_vector, mat_inverse, mat_mul};
 
+#[path = "sheet_convert.rs"]
+mod convert;
+pub use convert::{bend_edge_names, convert_body};
+
 // Bound the aggregate geometry, including sampled curves and intermediate clipping pieces.
 // These are work limits, never geometry truncation: a larger input returns a useful error.
 // Exact lines and arcs count once each (the planar booleans work on them whole); free-form