feat: edge flanges with their own angle and height per edge (#447)

One edge flange feature gave all its flanges one height and one angle. A
part whose flanges lean differently took one feature per angle, and
flanges of separate features don't close toward each other, so its
corners stayed open.

- sheet.flange (edge): an entry of `edges` is a point [x, y, z] as before,
  or {point, angle?, height?} whose angle and height (expressions, checked
  like the feature's) replace the feature's for that edge. Bad input is
  refused with the edge named. Before, the object form was read for its
  point and the rest was ignored without a word.
- The feature stores its edges as FlangeEdge. An edge without values of
  its own is written as the plain point it always was, so designs without
  them are read and written as before; an unknown key in an edge is
  refused, not dropped.
- The edges' values are feature inputs of their own (Edge angle, Edge
  height, after the feature's), so parameters, renames and
  parameters.change reach them. timeline.edit names the edges again when
  it changes them, so each value stays with its edge.
- SheetBody::add_flanges_each trims every edge by its own setback and
  adds the flanges. The corners between them close as between equal
  flanges: the closing already works from the two flanges it joins (each
  one's fold and leg), so the flat pattern follows by hand from the
  angles, the heights and the rule (the tests derive it).
- The Flange dialog shows a row per picked edge with an angle and a
  height box (empty: the dialog's value) once more than one edge is
  picked, and brings them back on Edit Feature.

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

crates/engine/src/cmd/edit.rs

@@ -322,6 +322,14 @@ fn edit_feature(s: &mut Session, p: &Value) -> Result<Value> {
         nf.edge_refs = solidcraft_doc::edge_refs(&before, body, a);
         nf.edge_names = solidcraft_doc::edge_names_for(&before, body, a);
     }
+    // New or reordered flange edges: their names now, so each edge's own angle and height stay
+    // with the edge they were given for.
+    if let (FeatureKind::SheetFlange { edges: a, .. }, FeatureKind::SheetFlange { edges: b, .. }) = (&nf.kind, &f.kind) {
+        let points = |e: &[solidcraft_doc::FlangeEdge]| e.iter().map(|x| x.point).collect::<Vec<_>>();
+        if points(a) != points(b) {
+            nf.edge_names = solidcraft_doc::sheet::sheet_edge_names(&s.model.state_before(id), &points(a));
+        }
+    }
     // Profiles picked by index or point are kept by their curves, as when the feature was made.
     if nf.kind.clone().profile_sels_mut() != f.kind.clone().profile_sels_mut() {
         super::features::stable_profiles(s, &mut nf.kind)?;