mesh: geometry.features, mesh.plan and mesh.plan.apply from the feature graph (#402)

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

crates/engine/src/cmd/relax.rs

@@ -52,6 +52,7 @@ const REMESH: &[&str] = &[
     "mesh.hex.sweep",
     "mesh.hex.mapped",
     "mesh.hex.blocks",
+    "mesh.plan.apply",
     "mesh.hex.octree",
     "mesh.cells",
     "mesh.block",