feat: add Excel-like grid editor for OCR overlay (Kombi mode step 6)

Backend: new grid_editor_api.py with build-grid endpoint that detects
bordered boxes, splits page into zones, clusters columns/rows per zone
from Kombi word positions. New DB column grid_editor_result JSONB.

Frontend: GridEditor component with editable HTML tables per zone,
column bold toggle, header row toggle, undo/redo, keyboard navigation
(Tab/Enter/Arrow), image overlay verification, and save/load.

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

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

@@ -0,0 +1,110 @@
+'use client'
+
+interface GridToolbarProps {
+  dirty: boolean
+  saving: boolean
+  canUndo: boolean
+  canRedo: boolean
+  showOverlay: boolean
+  onSave: () => void
+  onUndo: () => void
+  onRedo: () => void
+  onRebuild: () => void
+  onToggleOverlay: () => void
+}
+
+export function GridToolbar({
+  dirty,
+  saving,
+  canUndo,
+  canRedo,
+  showOverlay,
+  onSave,
+  onUndo,
+  onRedo,
+  onRebuild,
+  onToggleOverlay,
+}: GridToolbarProps) {
+  return (
+    <div className="flex items-center gap-2 flex-wrap">
+      {/* Undo / Redo */}
+      <div className="flex items-center gap-1 border-r border-gray-200 dark:border-gray-700 pr-2">
+        <button
+          onClick={onUndo}
+          disabled={!canUndo}
+          className="p-1.5 rounded hover:bg-gray-100 dark:hover:bg-gray-700 disabled:opacity-30 disabled:cursor-not-allowed"
+          title="Rueckgaengig (Ctrl+Z)"
+        >
+          <svg className="w-4 h-4" fill="none" viewBox="0 0 24 24" stroke="currentColor" strokeWidth={2}>
+            <path strokeLinecap="round" strokeLinejoin="round" d="M3 10h10a5 5 0 015 5v2M3 10l4-4M3 10l4 4" />
+          </svg>
+        </button>
+        <button
+          onClick={onRedo}
+          disabled={!canRedo}
+          className="p-1.5 rounded hover:bg-gray-100 dark:hover:bg-gray-700 disabled:opacity-30 disabled:cursor-not-allowed"
+          title="Wiederholen (Ctrl+Shift+Z)"
+        >
+          <svg className="w-4 h-4" fill="none" viewBox="0 0 24 24" stroke="currentColor" strokeWidth={2}>
+            <path strokeLinecap="round" strokeLinejoin="round" d="M21 10H11a5 5 0 00-5 5v2M21 10l-4-4M21 10l-4 4" />
+          </svg>
+        </button>
+      </div>
+
+      {/* Overlay toggle */}
+      <button
+        onClick={onToggleOverlay}
+        className={`flex items-center gap-1 px-2.5 py-1.5 text-xs rounded-md border transition-colors ${
+          showOverlay
+            ? 'bg-teal-50 dark:bg-teal-900/30 border-teal-300 dark:border-teal-700 text-teal-700 dark:text-teal-300'
+            : 'border-gray-200 dark:border-gray-700 text-gray-600 dark:text-gray-400 hover:bg-gray-50 dark:hover:bg-gray-700'
+        }`}
+        title="Grid auf Bild anzeigen"
+      >
+        <svg className="w-3.5 h-3.5" fill="none" viewBox="0 0 24 24" stroke="currentColor" strokeWidth={2}>
+          <path strokeLinecap="round" strokeLinejoin="round" d="M4 5a1 1 0 011-1h14a1 1 0 011 1v2a1 1 0 01-1 1H5a1 1 0 01-1-1V5zM4 13a1 1 0 011-1h6a1 1 0 011 1v6a1 1 0 01-1 1H5a1 1 0 01-1-1v-6zM16 13a1 1 0 011-1h2a1 1 0 011 1v6a1 1 0 01-1 1h-2a1 1 0 01-1-1v-6z" />
+        </svg>
+        Bild-Overlay
+      </button>
+
+      {/* Rebuild */}
+      <button
+        onClick={onRebuild}
+        className="flex items-center gap-1 px-2.5 py-1.5 text-xs rounded-md border border-gray-200 dark:border-gray-700 text-gray-600 dark:text-gray-400 hover:bg-gray-50 dark:hover:bg-gray-700 transition-colors"
+        title="Grid neu berechnen"
+      >
+        <svg className="w-3.5 h-3.5" fill="none" viewBox="0 0 24 24" stroke="currentColor" strokeWidth={2}>
+          <path strokeLinecap="round" strokeLinejoin="round" d="M4 4v5h.582m15.356 2A8.001 8.001 0 004.582 9m0 0H9m11 11v-5h-.581m0 0a8.003 8.003 0 01-15.357-2m15.357 2H15" />
+        </svg>
+        Neu berechnen
+      </button>
+
+      {/* Spacer */}
+      <div className="flex-1" />
+
+      {/* Save */}
+      <button
+        onClick={onSave}
+        disabled={!dirty || saving}
+        className={`flex items-center gap-1.5 px-3 py-1.5 text-xs font-medium rounded-md transition-colors ${
+          dirty
+            ? 'bg-teal-600 text-white hover:bg-teal-700'
+            : 'bg-gray-100 dark:bg-gray-800 text-gray-400 cursor-not-allowed'
+        }`}
+        title="Speichern (Ctrl+S)"
+      >
+        {saving ? (
+          <svg className="w-3.5 h-3.5 animate-spin" fill="none" viewBox="0 0 24 24">
+            <circle className="opacity-25" cx="12" cy="12" r="10" stroke="currentColor" strokeWidth="4" />
+            <path className="opacity-75" fill="currentColor" d="M4 12a8 8 0 018-8V0C5.373 0 0 5.373 0 12h4z" />
+          </svg>
+        ) : (
+          <svg className="w-3.5 h-3.5" fill="none" viewBox="0 0 24 24" stroke="currentColor" strokeWidth={2}>
+            <path strokeLinecap="round" strokeLinejoin="round" d="M8 7H5a2 2 0 00-2 2v9a2 2 0 002 2h14a2 2 0 002-2V9a2 2 0 00-2-2h-3m-1 4l-3 3m0 0l-3-3m3 3V4" />
+          </svg>
+        )}
+        {saving ? 'Speichert...' : dirty ? 'Speichern' : 'Gespeichert'}
+      </button>
+    </div>
+  )
+}