feat: Dewarp-Korrektur als Schritt 2 in OCR Pipeline (7 Schritte)

Implementiert Buchwoelbungs-Entzerrung mit zwei Methoden:
- Methode A: Vertikale-Kanten-Analyse (Sobel + Polynom 2. Grades)
- Methode B: Textzeilen-Baseline (Tesseract + Baseline-Kruemmung)
Beste Methode wird automatisch gewaehlt, manueller Slider (-3 bis +3).

Backend: 3 neue Endpoints (auto/manual dewarp, ground truth)
Frontend: StepDewarp + DewarpControls, Pipeline von 6 auf 7 Schritte

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

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

@@ -11,6 +11,8 @@ interface ImageCompareViewProps {
   showGrid: boolean
   showBinarized: boolean
   binarizedUrl: string | null
+  leftLabel?: string
+  rightLabel?: string
 }
 
 function MmGridOverlay() {
@@ -77,6 +79,8 @@ export function ImageCompareView({
   showGrid,
   showBinarized,
   binarizedUrl,
+  leftLabel,
+  rightLabel,
 }: ImageCompareViewProps) {
   const [leftError, setLeftError] = useState(false)
   const [rightError, setRightError] = useState(false)
@@ -87,7 +91,7 @@ export function ImageCompareView({
     <div className="grid grid-cols-1 lg:grid-cols-2 gap-4">
       {/* Left: Original */}
       <div className="space-y-2">
-        <h3 className="text-sm font-medium text-gray-500 dark:text-gray-400">Original (unbearbeitet)</h3>
+        <h3 className="text-sm font-medium text-gray-500 dark:text-gray-400">{leftLabel || 'Original (unbearbeitet)'}</h3>
         <div className="relative bg-gray-100 dark:bg-gray-900 rounded-lg overflow-hidden border border-gray-200 dark:border-gray-700"
              style={{ aspectRatio: '210/297' }}>
           {originalUrl && !leftError ? (
@@ -108,7 +112,7 @@ export function ImageCompareView({
       {/* Right: Deskewed with Grid */}
       <div className="space-y-2">
         <h3 className="text-sm font-medium text-gray-500 dark:text-gray-400">
-          {showBinarized ? 'Binarisiert' : 'Begradigt'} {showGrid && '+ Raster (mm)'}
+          {rightLabel || `${showBinarized ? 'Binarisiert' : 'Begradigt'}${showGrid ? ' + Raster (mm)' : ''}`}
         </h3>
         <div className="relative bg-gray-100 dark:bg-gray-900 rounded-lg overflow-hidden border border-gray-200 dark:border-gray-700"
              style={{ aspectRatio: '210/297' }}>