feat(props): editable block Name row + collapsible XYZ groups

- Block reference Name (Misc) is editable: the dropdown re-points the
  insert to another definition; typing a new name renames the definition
  everywhere (record re-key, Block marker, every INSERT reference).
  Anonymous (*) and xref blocks stay read-only, with the same guards
  added to Scene::rename_block.
- Custom single-control dropdown (text field + caret) built on the
  shared floating_below overlay so the list always opens downward,
  unlike iced's space-based menu placement.
- Consecutive "<Base> X/Y/Z" rows (Position, Scale, Start, Center, ...)
  collapse into one expandable summary row across all entities; the
  expand state persists across rebuilds and selection changes.
- The BEDIT block tab no longer offers the layout Rename/Delete
  context menu.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/scene/model/object.rs

@@ -17,6 +17,13 @@ pub enum PropValue {
         selected: String,
         options: Vec<String>,
     },
+    /// Editable text plus a dropdown of existing options (block reference
+    /// Name row): picking an option re-points the reference, submitting a
+    /// new name renames the definition.
+    EditChoice {
+        value: String,
+        options: Vec<String>,
+    },
     /// ACI/RGB/ByLayer/ByBlock color — rendered as a color picker.
     ColorChoice(AcadColor),
     /// Color varies across the current multi-selection.