feat: ImageLayoutEditor, arrow-key nav, multi-select bold, wider columns

- New ImageLayoutEditor: SVG overlay on original scan with draggable
  column dividers, horizontal guidelines (margins/header/footer),
  double-click to add columns, x-button to delete
- GridTable: MIN_COL_WIDTH 40→80px for better readability
- Arrow up/down keys navigate between rows in the grid editor
- Ctrl+Click for multi-cell selection, Ctrl+B to toggle bold on selection
- getAdjacentCell works for cells that don't exist yet (new rows/cols)
- deleteColumn now merges x-boundaries correctly
- Session restore fix: grid_editor_result/structure_result in session GET
- Footer row 3-state cycle, auto-create cells for empty footer rows
- Grid save/build/GT-mark now advance current_step=11

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

admin-lehrer/app/(admin)/ai/ocr-overlay/page.tsx

@@ -43,6 +43,7 @@ export default function OcrOverlayPage() {
 
   const searchParams = useSearchParams()
   const deepLinkHandled = useRef(false)
+  const gridSaveRef = useRef<(() => Promise<void>) | null>(null)
 
   useEffect(() => {
     loadSessions()
@@ -271,6 +272,10 @@ export default function OcrOverlayPage() {
     setGtSaving(true)
     setGtMessage('')
     try {
+      // Auto-save grid editor before marking GT (so DB has latest edits)
+      if (gridSaveRef.current) {
+        await gridSaveRef.current()
+      }
       const resp = await fetch(
         `${KLAUSUR_API}/api/v1/ocr-pipeline/sessions/${sessionId}/mark-ground-truth?pipeline=${mode}`,
         { method: 'POST' }
@@ -327,7 +332,7 @@ export default function OcrOverlayPage() {
           ) : null
         case 6:
           return mode === 'kombi' ? (
-            <StepGridReview sessionId={sessionId} onNext={handleNext} />
+            <StepGridReview sessionId={sessionId} onNext={handleNext} saveRef={gridSaveRef} />
           ) : null
         default:
           return null