mesh.block: mapped hex, tet and wedge blocks with curved edges; solve.probe at points

A structured mesh of a six-sided block from its corners, with circular
and elliptical edges (Gordon-Hall transfinite interpolation), grading,
named faces, edges and vertices as geometry tags, and joining to the
existing mesh face to face (refused otherwise). solve.probe takes "at"
points and reports the nearest node with a result.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NmAttHhUZTokgPeEJia8sm

crates/engine/src/cmd/mod.rs

@@ -1,5 +1,6 @@
 //! The command registry. Each area has its own module; [`ALL`] lists every command.
 
+mod block;
 pub(crate) mod deck;
 pub(crate) mod define;
 mod edit;
@@ -32,6 +33,7 @@ pub static ALL: &[CommandSpec] = &[
     mesh::SURFACE_CHECK,
     mesh::PLANAR,
     mesh::TET_GENERATE,
+    block::BLOCK,
     tags::TAG,
     tags::TAG_CLEAR,
     model::UNITS,