feat(builder): mobile-B touch editing -- selection toolbar, tap-to-add, swipe-dismiss

Phase B makes the Craft.js editor genuinely usable by touch on top of Phase
A's responsive shell, gated entirely behind useIsMobile()/<=768px:

- Extract useNodeActions(nodeId) out of ContextMenu.tsx (move/duplicate/
  delete/select-parent), shared by the desktop right-click menu (behavior
  unchanged) and the new mobile MobileSelectionToolbar.
- MobileSelectionToolbar: bottom-fixed selection toolbar (Move Up/Down,
  Duplicate, Select Parent, Edit Styles, two-tap Delete confirm), hidden
  while a sheet is open.
- BlocksPanel: tap-to-add on mobile (insert after selection, close sheet,
  select + scroll the new node into view); desktop drag/double-click
  unchanged.
- LayersPanel rows >=44px on mobile; HeadCodeModal portaled to document.body
  (same fix TemplateModal already had); BottomSheet gets swipe-to-dismiss
  and on-screen-keyboard clearance via a new useVisualViewportInsets hook.

Also fixes two pre-existing bugs surfaced only by driving a real Craft.js
document with Playwright touch input (masked by tests that mock
@craftjs/core): regenerateTreeIds structuredClone'd a live node's whole
data object, including the component function reference in data.type,
throwing DataCloneError and silently breaking Duplicate/Paste for every
node type; and an earlier useNodeActions draft cached canMoveUp/canMoveDown
inside a useEditor collector closed over nodeId, which goes stale for one
render whenever the selection changes without an unrelated store event.

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

craft/src/hooks/useVisualViewport.ts

@@ -0,0 +1,55 @@
+import { useEffect, useState } from 'react';
+
+export interface VisualViewportInsets {
+  /** The visual viewport's current height (shrinks when the on-screen
+   *  keyboard opens). Falls back to `window.innerHeight` when
+   *  `visualViewport` isn't supported. */
+  height: number;
+  /** Extra inset a `position: fixed`, bottom-anchored element should add to
+   *  its own `bottom` offset to stay clear of the on-screen keyboard --
+   *  `window.innerHeight` minus the visual viewport's bottom edge (its
+   *  height + offsetTop). Zero whenever no keyboard is open, or
+   *  `visualViewport` isn't supported (a safe no-op fallback). */
+  keyboardInset: number;
+}
+
+const ZERO_INSETS: VisualViewportInsets = { height: 0, keyboardInset: 0 };
+
+function computeInsets(): VisualViewportInsets {
+  if (typeof window === 'undefined') return ZERO_INSETS;
+  const vv = window.visualViewport;
+  if (!vv) return { height: window.innerHeight, keyboardInset: 0 };
+  const keyboardInset = Math.max(0, window.innerHeight - (vv.height + vv.offsetTop));
+  return { height: vv.height, keyboardInset };
+}
+
+/**
+ * Tracks `window.visualViewport`'s height/offset (item 5, Phase B) so
+ * `BottomSheet` can stay clear of the on-screen keyboard. `position: fixed`
+ * elements are positioned against the LAYOUT viewport, which does NOT shrink
+ * when a mobile keyboard opens -- only the visual viewport does -- so a
+ * bottom-anchored sheet's inputs can otherwise end up hidden underneath the
+ * keyboard with no visual indication anything is wrong.
+ *
+ * Guards for browsers without `visualViewport` (older WebViews): falls back
+ * to `{ height: window.innerHeight, keyboardInset: 0 }`, i.e. a no-op, so
+ * the sheet just keeps its existing (keyboard-unaware) sizing there.
+ */
+export function useVisualViewportInsets(): VisualViewportInsets {
+  const [insets, setInsets] = useState<VisualViewportInsets>(computeInsets);
+
+  useEffect(() => {
+    if (typeof window === 'undefined' || !window.visualViewport) return;
+    const vv = window.visualViewport;
+    const handleChange = () => setInsets(computeInsets());
+    handleChange();
+    vv.addEventListener('resize', handleChange);
+    vv.addEventListener('scroll', handleChange);
+    return () => {
+      vv.removeEventListener('resize', handleChange);
+      vv.removeEventListener('scroll', handleChange);
+    };
+  }, []);
+
+  return insets;
+}