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/app/mod.rs

@@ -1671,6 +1671,11 @@ pub enum Message {
     },
     /// User committed a geometry/common field edit (Enter pressed).
     PropGeomCommit(&'static str),
+    /// Toggle a collapsed coordinate group ("Position", "Scale", …) open or
+    /// closed in the Properties panel, keyed `section:base`.
+    PropGroupToggle(String),
+    /// Toggle the editable-dropdown (block Name) option list open/closed.
+    PropEditChoiceToggle,
     /// User is typing in a block-attribute value field (live buffer update),
     /// keyed by the attribute tag.
     PropAttrInput { tag: String, value: String },