Engine: model.boundary_condition.symmetry on a datum plane

A symmetry condition (zero normal displacement, zero rotation about the
in-plane axes) on a datum plane normal to X, Y or Z, with its set given or made
of the open design's faces on the plane (a partition's cut faces), so half a
symmetric part is solved as a half. Half a 40 mm bar cut at its mid-width, with
the condition and half the load, bends as the whole bar to 2e-12 with half the
reaction. Inclined planes are refused as not supported yet.

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

crates/engine/src/catalogue.rs

@@ -387,7 +387,7 @@ pub static CATALOGUE: &[Capability] = &[
         Loads,
         "Boundary Conditions",
         "Fixed, displacement or symmetry condition on a set or reference point",
-        &["model.boundary_condition.edit", "model.boundary_condition.delete"],
+        &["model.boundary_condition.edit", "model.boundary_condition.delete", "model.boundary_condition.symmetry"],
     ),
     ready_more(
         "model.load.create",