engine: mesh.node.move moves nodes by a vector or to a point

The grabbed nodes (listed, on B-rep faces, or a sphere's) move; the nodes
within the radius follow by a falloff or harmonically; nodes stay on the
geometry as Relax Nodes moves them; the move is scaled back until no element
inverts. The reply gives the region's scaled Jacobian before and after and the
elements that got worse and better. One undo step. Toolbar entry Move Nodes
(Mesh, Improve) with its own icon.

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

crates/engine/src/cmd/mod.rs

@@ -18,12 +18,15 @@ pub(crate) mod mesh;
 
 pub use datum::edit_params as datum_edit_params;
 pub use datum::preview as datum_preview;
+pub use fieldcraft_mesh::relax::{ElementChange, Moved as NodeMoved};
 pub use mesh::analytic_surfaces;
+pub use node_move::{Prepared as NodeMovePrepared, nearest_node as node_move_nearest, prepare as node_move_prepare};
 pub use nodes::merge_preview as node_merge_preview;
 pub use plan::untagged_faces;
 pub use relax::{Preview as RelaxPreview, preview as relax_preview, sphere as relax_sphere};
 mod mirror;
 mod model;
+pub(crate) mod node_move;
 pub(crate) mod nodes;
 pub(crate) mod octree;
 pub(crate) mod plan;
@@ -121,6 +124,7 @@ pub static ALL: &[CommandSpec] = &[
     nodes::RENUMBER,
     relax::RELAX,
     relax::APPLY,
+    node_move::MOVE,
     tags::TAG,
     tags::TAG_CLEAR,
     model::UNITS,