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/selection.rs

@@ -293,6 +293,7 @@ impl Scene {
                     PropValue::ReadOnly(s) | PropValue::EditText(s) => s,
                     PropValue::LayerChoice(s) => s,
                     PropValue::Choice { selected, .. } => selected,
+                    PropValue::EditChoice { value, .. } => value,
                     PropValue::ColorChoice(c) => Self::format_color(c),
                     PropValue::LwChoice(lw) => Self::format_lineweight(lw),
                     PropValue::LinetypeChoice(s) => s,