sitesmith: route ColumnLayout children through linkedNodes (Invariant fix)

ColumnLayout's render uses <Element id="col-0" is={Container} canvas>
which expects the columns to live in linkedNodes, not data.nodes. The
AI nests its column containers as direct children, so they'd land in
data.nodes — Craft.js's render ignores them (the layout draws fresh
empty Elements), but the orphaned children remain in state with
parent: <columnlayout-id>. Any subsequent toNodeTree walk then trips
on this inconsistency and the uncaught Invariant kills the editor.

Normalizer added in two places — treeToState (for scope=site/page
replaces) and buildNodeTree (for scope=section inserts and patch ops):
when we see a ColumnLayout with direct children, move them into
linkedNodes keyed col-0/col-1/col-2..., clear data.nodes, set the
column nodes' isCanvas to true (they hold content), and sync the
"columns" prop to the actual count.

craft/src/state/PageContext.tsx

@@ -325,6 +325,24 @@ export const PageProvider: React.FC<{ children: ReactNode }> = ({ children }) =>
       for (const child of node.nodes ?? []) {
         childIds.push(walk(child, id));
       }
+      // ColumnLayout uses Craft.js linkedNodes with fixed ids (col-0, col-1, ...).
+      // The AI emits children as direct `nodes`, but ColumnLayout's render ignores
+      // them and creates fresh column Elements — the AI's children become orphans
+      // and any subsequent toNodeTree walk hits an Invariant. Move direct children
+      // into linkedNodes so they render in the columns the user actually sees.
+      if (typeName === 'ColumnLayout' && childIds.length > 0) {
+        const linked: Record<string, string> = {};
+        childIds.forEach((cid, i) => {
+          linked[`col-${i}`] = cid;
+          if (nodes[cid]) (nodes[cid] as any).isCanvas = true; // columns are canvases
+        });
+        (nodes[id] as any).nodes = [];
+        (nodes[id] as any).linkedNodes = linked;
+        // Reflect the actual column count on the component so its render matches.
+        const cur = (nodes[id] as any).props || {};
+        if (!cur.columns || cur.columns !== childIds.length) cur.columns = childIds.length;
+        (nodes[id] as any).props = cur;
+      }
       return id;
     };
     const rootId = walk(tree, null);