feat: add Woerterbuch category + column add/delete in grid editor

- New document category "Woerterbuch" (frontend type + backend validation)
- Column delete: hover column header → red "x" button (with confirmation)
- Column add: hover column header → "+" button inserts after that column
- Both operations support undo/redo, update cell IDs and summary
- Available in both GridEditor and StepGridReview (Kombi last step)

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

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

@@ -32,6 +32,8 @@ export function GridEditor({ sessionId, onNext }: GridEditorProps) {
     canUndo,
     canRedo,
     getAdjacentCell,
+    deleteColumn,
+    addColumn,
   } = useGridEditor(sessionId)
 
   const [showOverlay, setShowOverlay] = useState(false)
@@ -219,6 +221,8 @@ export function GridEditor({ sessionId, onNext }: GridEditorProps) {
                   onToggleColumnBold={toggleColumnBold}
                   onToggleRowHeader={toggleRowHeader}
                   onNavigate={handleNavigate}
+                  onDeleteColumn={deleteColumn}
+                  onAddColumn={addColumn}
                 />
               </div>
             ) : (