fix(copy): copied associative hatches follow the copied boundary

The copy kept the source boundary handles, so editing the source
regenerated the copy onto the source outline and it seemed to vanish.

Fixes #1370

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/scene/modify.rs

@@ -810,6 +810,7 @@ impl Scene {
         // entry as targeted object deltas inside copy_complete_groups.
         self.copy_complete_groups(&handle_map);
         self.copy_dimension_associations(&handle_map);
+        self.copy_hatch_associations(&handle_map);
         // The copies are new handles (natural memo misses, tessellated fresh)
         // and reference only already-cached blocks — no block defn changes.
         // Report them as additions so derived caches patch in exactly the copies.