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/StepDewarp.tsx

@@ -0,0 +1,150 @@
+'use client'
+
+import { useCallback, useEffect, useState } from 'react'
+import type { DewarpResult, DewarpGroundTruth } from '@/app/(admin)/ai/ocr-pipeline/types'
+import { DewarpControls } from './DewarpControls'
+import { ImageCompareView } from './ImageCompareView'
+
+const KLAUSUR_API = '/klausur-api'
+
+interface StepDewarpProps {
+  sessionId: string | null
+  onNext: () => void
+}
+
+export function StepDewarp({ sessionId, onNext }: StepDewarpProps) {
+  const [dewarpResult, setDewarpResult] = useState<DewarpResult | null>(null)
+  const [dewarping, setDewarping] = useState(false)
+  const [applying, setApplying] = useState(false)
+  const [showGrid, setShowGrid] = useState(true)
+  const [error, setError] = useState<string | null>(null)
+
+  // Auto-trigger dewarp when component mounts with a sessionId
+  useEffect(() => {
+    if (!sessionId || dewarpResult) return
+
+    const runDewarp = async () => {
+      setDewarping(true)
+      setError(null)
+      try {
+        const res = await fetch(`${KLAUSUR_API}/api/v1/ocr-pipeline/sessions/${sessionId}/dewarp`, {
+          method: 'POST',
+        })
+        if (!res.ok) {
+          const err = await res.json().catch(() => ({ detail: res.statusText }))
+          throw new Error(err.detail || 'Entzerrung fehlgeschlagen')
+        }
+        const data: DewarpResult = await res.json()
+        data.dewarped_image_url = `${KLAUSUR_API}${data.dewarped_image_url}`
+        setDewarpResult(data)
+      } catch (e) {
+        setError(e instanceof Error ? e.message : 'Unbekannter Fehler')
+      } finally {
+        setDewarping(false)
+      }
+    }
+
+    runDewarp()
+  }, [sessionId, dewarpResult])
+
+  const handleManualDewarp = useCallback(async (scale: number) => {
+    if (!sessionId) return
+    setApplying(true)
+    setError(null)
+
+    try {
+      const res = await fetch(`${KLAUSUR_API}/api/v1/ocr-pipeline/sessions/${sessionId}/dewarp/manual`, {
+        method: 'POST',
+        headers: { 'Content-Type': 'application/json' },
+        body: JSON.stringify({ scale }),
+      })
+      if (!res.ok) throw new Error('Manuelle Entzerrung fehlgeschlagen')
+
+      const data = await res.json()
+      setDewarpResult((prev) =>
+        prev
+          ? {
+              ...prev,
+              method_used: data.method_used,
+              scale_applied: data.scale_applied,
+              dewarped_image_url: `${KLAUSUR_API}${data.dewarped_image_url}?t=${Date.now()}`,
+            }
+          : null,
+      )
+    } catch (e) {
+      setError(e instanceof Error ? e.message : 'Fehler')
+    } finally {
+      setApplying(false)
+    }
+  }, [sessionId])
+
+  const handleGroundTruth = useCallback(async (gt: DewarpGroundTruth) => {
+    if (!sessionId) return
+    try {
+      await fetch(`${KLAUSUR_API}/api/v1/ocr-pipeline/sessions/${sessionId}/ground-truth/dewarp`, {
+        method: 'POST',
+        headers: { 'Content-Type': 'application/json' },
+        body: JSON.stringify(gt),
+      })
+    } catch (e) {
+      console.error('Ground truth save failed:', e)
+    }
+  }, [sessionId])
+
+  if (!sessionId) {
+    return (
+      <div className="flex flex-col items-center justify-center py-16 text-center">
+        <div className="text-5xl mb-4">🔧</div>
+        <h3 className="text-lg font-medium text-gray-700 dark:text-gray-300 mb-2">
+          Schritt 2: Entzerrung (Dewarp)
+        </h3>
+        <p className="text-gray-500 dark:text-gray-400 max-w-md">
+          Bitte zuerst Schritt 1 (Begradigung) abschliessen.
+        </p>
+      </div>
+    )
+  }
+
+  const deskewedUrl = `${KLAUSUR_API}/api/v1/ocr-pipeline/sessions/${sessionId}/image/deskewed`
+  const dewarpedUrl = dewarpResult?.dewarped_image_url ?? null
+
+  return (
+    <div className="space-y-4">
+      {/* Loading indicator */}
+      {dewarping && (
+        <div className="flex items-center gap-2 text-teal-600 dark:text-teal-400 text-sm">
+          <div className="animate-spin w-4 h-4 border-2 border-teal-500 border-t-transparent rounded-full" />
+          Entzerrung laeuft (beide Methoden)...
+        </div>
+      )}
+
+      {/* Image comparison: deskewed (left) vs dewarped (right) */}
+      <ImageCompareView
+        originalUrl={deskewedUrl}
+        deskewedUrl={dewarpedUrl}
+        showGrid={showGrid}
+        showBinarized={false}
+        binarizedUrl={null}
+        leftLabel="Begradigt (nach Deskew)"
+        rightLabel={`Entzerrt${showGrid ? ' + Raster (mm)' : ''}`}
+      />
+
+      {/* Controls */}
+      <DewarpControls
+        dewarpResult={dewarpResult}
+        showGrid={showGrid}
+        onToggleGrid={() => setShowGrid((v) => !v)}
+        onManualDewarp={handleManualDewarp}
+        onGroundTruth={handleGroundTruth}
+        onNext={onNext}
+        isApplying={applying}
+      />
+
+      {error && (
+        <div className="p-3 bg-red-50 dark:bg-red-900/20 text-red-600 dark:text-red-400 rounded-lg text-sm">
+          {error}
+        </div>
+      )}
+    </div>
+  )
+}