Block Attribute Manager: one undo step per Apply

Live changes are taken back quietly before Apply, OK or Sync write the
list again, so each leaves exactly one undo step even when something
closed the open live step in between; Cancel takes them back without a
command-line notice. References keep their values through renames made
live.

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

src/app/history.rs

@@ -1287,6 +1287,12 @@ impl OpenCADStudio {
     }
 
     pub(super) fn undo_steps(&mut self, steps: usize) {
+        self.undo_steps_reported(steps, true);
+    }
+
+    /// [`Self::undo_steps`]; `report` false takes the steps back without
+    /// the command-line notice (a dialog withdrawing its own live changes).
+    pub(super) fn undo_steps_reported(&mut self, steps: usize, report: bool) {
         let i = self.active_tab;
         self.finish_pending_history(i);
         let available = self.tabs[i].history.undo_stack.len();
@@ -1353,8 +1359,10 @@ impl OpenCADStudio {
             native_graph_changed,
             &changes,
         );
-        self.command_line
-            .push_output(crate::tf!("Undo: {last_label}").as_ref());
+        if report {
+            self.command_line
+                .push_output(crate::tf!("Undo: {last_label}").as_ref());
+        }
     }
 
     pub(super) fn redo_steps(&mut self, steps: usize) {