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 <[email protected]>

src/ui/window/attman_dialog.rs

@@ -179,9 +179,10 @@ pub struct AttManBlock {
 pub struct AttManRow {
     /// The definition object in the block.
     pub handle: Handle,
-    /// The tag the definition had when the block was loaded, for keeping the
-    /// references' values when it is renamed.
+    /// The tag the definition had when the block was loaded or applied.
     pub original_tag: String,
+    /// The tag the references hold now (changed by live writes).
+    pub live_tag: String,
     /// The working copy.
     pub def: AttributeDefinition,
 }