geometry: meshes go with the bodies a partition change removes (#385)

Deleting, suppressing or editing a partition (or its datum), or cutting a
meshed body, removes the meshes of the bodies that are gone, reported as
replaced, in the same undo step. model.check lists meshes of partition
cells the open design no longer has (a model saved before the cut
changed), and mesh.clear removes them, or the meshes of named bodies.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UhhZMBTviDQxZvwnyP89fo

crates/engine/src/cmd/forms.rs

@@ -1129,6 +1129,10 @@ pub const CELLS: &[Field] = &[
     TOLERANCE,
 ];
 
+pub const CLEAR_MESH: &[Field] = &[references("bodies", "Bodies", C::Body)
+    .help("The bodies whose meshes go. When none is ticked: the meshes of bodies the open design no longer has because its partitions changed (model.check lists them).")
+    .hint("the bodies partitions removed")];
+
 pub const MIRROR: &[Field] = &[
     json("plane", "Plane")
         .help("The mirror plane: a datum plane's name, or a point and normal as JSON.")