Fix construction-plane references in mirror, section, and sketches (#99)

Accept construction planes by name or feature ID, preserve parametric mirror references, and reject invalid plane inputs. Retain both mirror-plane and primitive-point regression test modules after resolving the conflict with main.

Validation: cargo xtask ci passed, including 282 engine tests, 138 UI tests, 62 UI scenarios, and WebAssembly.

crates/engine/src/tests.rs

@@ -36,6 +36,7 @@ fn join_extrude_from_a_chamfered_top_face() {
 }
 
 mod component_frames;
+mod mirror_planes;
 mod primitive_points;
 mod robustness;