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/StepLlmReview.tsx

@@ -387,7 +387,7 @@ export function StepLlmReview({ sessionId, onNext }: StepLlmReviewProps) {
       <div className="flex items-center justify-between">
         <div>
           <h3 className="text-base font-medium text-gray-700 dark:text-gray-300">
-            Schritt 6: OCR-Zeichenkorrektur
+            Schritt 6: Korrektur
           </h3>
           <p className="text-xs text-gray-400 mt-0.5">
             {status === 'ready' && `${vocabEntries.length} Eintraege bereit zur Pruefung`}
@@ -405,7 +405,7 @@ export function StepLlmReview({ sessionId, onNext }: StepLlmReviewProps) {
           {status === 'ready' && (
             <button onClick={runReview}
               className="px-5 py-2 bg-teal-600 text-white rounded-lg hover:bg-teal-700 transition-colors text-sm font-medium">
-              Zeichenkorrektur starten
+              Korrektur starten
             </button>
           )}
           {status === 'running' && (