perf: AABB snap pre-rejection via acadrust bounding_box() (Option K upgrade)

Add `aabb: [f32; 4]` field to WireModel (world-space 2-D bounding box).
In tessellate_entity() set each wire's AABB from e.as_entity().bounding_box()
via new entity_aabb() helper; Insert sub-entities each get their own AABB.
Preview/interim wires and any entity returning a zero-extent default box get
UNBOUNDED_AABB so they are never pre-rejected.

Replace the chord-sphere heuristic in Snapper::wire_in_range() with a proper
AABB vs snap-circle overlap test.  The new check is four scalar comparisons and
correctly handles closed curves (circles, arcs) which the chord-sphere approach
had to special-case.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/app/update.rs

@@ -1261,6 +1261,7 @@ impl H7CAD {
                                     snap_pts: vec![],
                                     tangent_geoms: vec![],
                                     key_vertices: vec![],
+                                    aabb: crate::scene::WireModel::UNBOUNDED_AABB,
                                 };
                                 previews.push(guide);
                             }