fix: three OCR pipeline UX improvements

1. Rename Step 6 label to "Korrektur" (was "OCR-Zeichenkorrektur")
2. Move _fix_character_confusion from pipeline Step 1 into
   llm_review_entries_streaming so corrections are visible in the UI:
   char changes (| → I, 1 → I, 8 → B) are now emitted as a batch event
   right after the meta event, appearing in the corrections list
3. StepReconstruction: all cells (including empty) are now rendered as
   editable inputs — removed filter that hid empty cells from the editor

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

admin-lehrer/components/ocr-pipeline/StepReconstruction.tsx

@@ -35,8 +35,7 @@ export function StepReconstruction({ sessionId, onNext }: StepReconstructionProp
   const [undoStack, setUndoStack] = useState<UndoAction[]>([])
   const [redoStack, setRedoStack] = useState<UndoAction[]>([])
 
-  // All cells including empty ones (for empty field highlighting)
-  const [allCells, setAllCells] = useState<EditableCell[]>([])
+  // (allCells removed — cells now contains all cells including empty ones)
 
   const containerRef = useRef<HTMLDivElement>(null)
   const imageRef = useRef<HTMLImageElement>(null)
@@ -82,8 +81,7 @@ export function StepReconstruction({ sessionId, onNext }: StepReconstructionProp
         colIndex: c.col_index,
       }))
 
-      setAllCells(allEditableCells)
-      setCells(allEditableCells.filter(c => c.text.trim() !== ''))
+      setCells(allEditableCells)
       setEditedTexts(new Map())
       setUndoStack([])
       setRedoStack([])
@@ -191,7 +189,7 @@ export function StepReconstruction({ sessionId, onNext }: StepReconstructionProp
   const emptyCellIds = useMemo(() => {
     const required = new Set(['column_en', 'column_de'])
     const ids = new Set<string>()
-    for (const cell of allCells) {
+    for (const cell of cells) {
       if (required.has(cell.colType) && !cell.text.trim()) {
         ids.add(cell.cellId)
       }
@@ -429,7 +427,7 @@ export function StepReconstruction({ sessionId, onNext }: StepReconstructionProp
           />
 
           {/* Empty field markers */}
-          {showEmptyHighlight && allCells
+          {showEmptyHighlight && cells
             .filter(c => emptyCellIds.has(c.cellId))
             .map(cell => (
               <div