perf(scene): make geometry edits incremental

Avoid full document, cache, and GPU rebuilds for entity deltas so add, delete, history, selection, and live polyline edits stay responsive on large drawings.

src/scene/modify.rs

@@ -410,12 +410,9 @@ impl Scene {
             }
         }
 
-        let copied_groups = self.copy_complete_groups(&handle_map);
-        if copied_groups > 0 && self.is_recording_undo() {
-            // Group copies add Group objects / dictionary entries, which a pure
-            // entity delta cannot restore.
-            self.poison_undo_recording();
-        }
+        // Complete group copies record their new Group objects and dictionary
+        // entry as targeted object deltas inside copy_complete_groups.
+        self.copy_complete_groups(&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.