test(builder): cover useVisualViewport; fix: disable Select-Parent at ROOT in desktop context menu

- useVisualViewport.test.tsx: covers the visualViewport-undefined fallback,
  the keyboardInset math on a mocked visualViewport resize, and
  listener add/remove (resize + scroll) across mount/unmount.
- ContextMenu.tsx: Select Parent was only disabled at isRoot, so selecting
  a top-level section and choosing Select Parent silently landed on the
  un-editable ROOT (no outline, no toolbar) -- a dead end. Switched the
  guard to useNodeActions' canSelectParent (false whenever the node's
  parent is ROOT or missing), matching the mobile selection toolbar's
  existing identical guard.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

craft/src/panels/context-menu/ContextMenu.tsx

@@ -195,7 +195,12 @@ export const ContextMenu: React.FC<ContextMenuProps> = ({
       label: 'Select Parent',
       icon: 'level-up',
       action: selectParent,
-      disabled: isRoot,
+      // Not just `isRoot`: the real dead-end is when nodeId's PARENT is
+      // ROOT (selecting a top-level section -> Select Parent would only
+      // select the page-wide, un-editable ROOT -- no outline, no toolbar).
+      // `canSelectParent` (useNodeActions) already encodes that and matches
+      // the mobile selection toolbar's identical guard.
+      disabled: !nodeActions.canSelectParent,
       dividerAfter: true,
     },
     {