mesh.hex.blocks: one conforming hex mesh of a design split into blocks

Meshes the open design's bodies (or the listed ones) as the cells of one
conforming all-hex mesh with one size and tessellation tolerance for all;
elements carry their cell's body, boundary faces its B-rep faces. A cell
that is no block, or cells that touch without sharing whole faces, is an
error naming the bodies. Catalogue entry with its VectorCraft icon, the
MCP mesh tool's hex_blocks method, docs/features.md.

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

crates/engine/src/cmd/mod.rs

@@ -40,6 +40,7 @@ pub static ALL: &[CommandSpec] = &[
     hex::HEX_GENERATE,
     hex::HEX_SWEEP,
     hex::HEX_MAPPED,
+    hex::HEX_BLOCKS,
     tags::TAG,
     tags::TAG_CLEAR,
     model::UNITS,