Engine: geometry.datum.point; planes and axes through datum points; datum edits and cascading delete

A datum point by coordinates, at a mesh vertex, a fraction along a
design edge, at a face's centre, or where a datum axis crosses a datum
plane. Datum planes take three datum points or a normal to a datum axis;
axes take two datum points. geometry.datum.edit, .axis.edit and
.point.edit redefine a datum of their kind (partitions cut again);
geometry.datum.delete with cascade also deletes the partitions that cut
by it. The ribbon shows Datum Plane, Datum Axis, Datum Point and
Partition, each with its own icon; edit and delete leave the ribbon
(still commands, claimed by their entries).

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

crates/engine/src/cmd/mod.rs

@@ -13,6 +13,7 @@ mod geometry;
 mod hex;
 pub(crate) mod mesh;
 
+pub use datum::edit_params as datum_edit_params;
 pub use mesh::analytic_surfaces;
 mod mirror;
 mod model;
@@ -41,6 +42,10 @@ pub static ALL: &[CommandSpec] = &[
     geometry::IMPORT_MESH,
     datum::DATUM_PLANE,
     datum::DATUM_AXIS,
+    datum::DATUM_POINT,
+    datum::DATUM_EDIT,
+    datum::DATUM_AXIS_EDIT,
+    datum::DATUM_POINT_EDIT,
     datum::DATUM_DELETE,
     datum::PARTITION,
     datum::PARTITION_DELETE,