Fix vsplit side-by-side rendering: invalid TypeScript type annotation

Changed `typeof grid.zones[][]` to `GridZone[][]` which was causing
a silent build error, preventing the vsplit zone grouping logic from
being compiled into the production bundle.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

admin-lehrer/components/grid-editor/GridEditor.tsx

@@ -2,6 +2,7 @@
 
 import { useCallback, useEffect, useState } from 'react'
 import { useGridEditor } from './useGridEditor'
+import type { GridZone } from './types'
 import { GridToolbar } from './GridToolbar'
 import { GridTable } from './GridTable'
 import { GridImageOverlay } from './GridImageOverlay'
@@ -190,7 +191,7 @@ export function GridEditor({ sessionId, onNext }: GridEditorProps) {
       <div className="space-y-4">
         {(() => {
           // Group consecutive zones with same vsplit_group
-          const groups: typeof grid.zones[][] = []
+          const groups: GridZone[][] = []
           for (const zone of grid.zones) {
             const prev = groups[groups.length - 1]
             if (