feat: 180°-Rotation fuer Pixel-Matching im Overlay-Modus

- usePixelWordPositions: neuer rotation-Parameter (0 | 180)
- Bei 180°: Bild auf Canvas rotiert, Zell-Koordinaten transformiert,
  Cluster-Positionen zurueck-gespiegelt
- StepReconstruction: 180°-Toggle-Button in Overlay-Toolbar
- Default 180° bei Parent-Sessions mit Boxen
- Linkes Originalbild wird ebenfalls CSS-rotiert

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

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

@@ -59,6 +59,7 @@ export function StepReconstruction({ sessionId, onNext }: StepReconstructionProp
   const [imageNaturalSize, setImageNaturalSize] = useState<{ w: number; h: number } | null>(null)
   const [fontScale, setFontScale] = useState(0.7)
   const [globalBold, setGlobalBold] = useState(false)
+  const [imageRotation, setImageRotation] = useState<0 | 180>(0)
   const reconRef = useRef<HTMLDivElement>(null)
   const [reconWidth, setReconWidth] = useState(0)
 
@@ -70,6 +71,7 @@ export function StepReconstruction({ sessionId, onNext }: StepReconstructionProp
     overlayImageUrl,
     mergedGridCells,
     editorMode === 'overlay',
+    imageRotation,
   )
 
   // Track reconstruction container width for font size calculation
@@ -138,6 +140,7 @@ export function StepReconstruction({ sessionId, onNext }: StepReconstructionProp
       const hasBoxes = subSessions.length > 0 && zones.some(z => z.zone_type === 'box')
 
       setIsParentWithBoxes(hasBoxes)
+      if (hasBoxes) setImageRotation(180) // Default: rotate for correct pixel matching
 
       if (columnResult?.columns) setParentColumns(columnResult.columns)
       if (rowResult?.rows) setParentRows(rowResult.rows)
@@ -493,6 +496,7 @@ export function StepReconstruction({ sessionId, onNext }: StepReconstructionProp
               src={dewarpedUrl}
               alt="Original"
               className="w-full h-auto"
+              style={imageRotation === 180 ? { transform: 'rotate(180deg)' } : undefined}
               onLoad={(e) => {
                 const img = e.target as HTMLImageElement
                 setImageNaturalSize({ w: img.naturalWidth, h: img.naturalHeight })
@@ -775,6 +779,17 @@ export function StepReconstruction({ sessionId, onNext }: StepReconstructionProp
               >
                 B
               </button>
+              <button
+                onClick={() => setImageRotation(r => r === 0 ? 180 : 0)}
+                className={`px-2 py-1 text-xs rounded border transition-colors ${
+                  imageRotation === 180
+                    ? 'bg-teal-600 text-white border-teal-600'
+                    : 'bg-white dark:bg-gray-700 text-gray-600 dark:text-gray-400 border-gray-300 dark:border-gray-600'
+                }`}
+                title="Bild 180° drehen"
+              >
+                180°
+              </button>
               <div className="w-px h-5 bg-gray-300 dark:bg-gray-600 mx-1" />
             </>
           )}

admin-lehrer/components/ocr-pipeline/usePixelWordPositions.ts

@@ -12,12 +12,17 @@ export interface WordPosition {
  * Shared hook: analyse dark-pixel clusters on an image to determine
  * the exact horizontal position & auto-font-size of word groups in each cell.
  *
+ * When rotation=180, the image is rotated 180° before pixel analysis.
+ * Cell coordinates are transformed to the rotated space for reading,
+ * and cluster positions are mirrored back to the original coordinate system.
+ *
  * Returns a Map<cell_id, WordPosition[]>.
  */
 export function usePixelWordPositions(
   imageUrl: string,
   cells: GridCell[],
   active: boolean,
+  rotation: 0 | 180 = 0,
 ): Map<string, WordPosition[]> {
   const [cellWordPositions, setCellWordPositions] = useState<Map<string, WordPosition[]>>(new Map())
 
@@ -27,12 +32,24 @@ export function usePixelWordPositions(
     const img = new Image()
     img.crossOrigin = 'anonymous'
     img.onload = () => {
+      const imgW = img.naturalWidth
+      const imgH = img.naturalHeight
+
       const canvas = document.createElement('canvas')
-      canvas.width = img.naturalWidth
-      canvas.height = img.naturalHeight
+      canvas.width = imgW
+      canvas.height = imgH
       const ctx = canvas.getContext('2d')
       if (!ctx) return
-      ctx.drawImage(img, 0, 0)
+
+      if (rotation === 180) {
+        // Draw image rotated 180°
+        ctx.translate(imgW, imgH)
+        ctx.rotate(Math.PI)
+        ctx.drawImage(img, 0, 0)
+        ctx.setTransform(1, 0, 0, 1, 0, 0) // reset transform for measureText
+      } else {
+        ctx.drawImage(img, 0, 0)
+      }
 
       const refFontSize = 40
       const fontFam = "'Liberation Sans', Arial, sans-serif"
@@ -46,14 +63,24 @@ export function usePixelWordPositions(
         // Split by 3+ whitespace into word-groups
         const groups = cell.text.split(/\s{3,}/).map(s => s.trim()).filter(Boolean)
 
-        // Pixel region for this cell
-        const imgW = img.naturalWidth
-        const imgH = img.naturalHeight
-        const cx = Math.round(cell.bbox_pct.x / 100 * imgW)
-        const cy = Math.round(cell.bbox_pct.y / 100 * imgH)
+        // Cell pixel region — when rotated 180°, transform coordinates
+        let cx: number, cy: number
         const cw = Math.round(cell.bbox_pct.w / 100 * imgW)
         const ch = Math.round(cell.bbox_pct.h / 100 * imgH)
+
+        if (rotation === 180) {
+          // In rotated image: (x,y) maps to (W-x-w, H-y-h)
+          cx = Math.round((100 - cell.bbox_pct.x - cell.bbox_pct.w) / 100 * imgW)
+          cy = Math.round((100 - cell.bbox_pct.y - cell.bbox_pct.h) / 100 * imgH)
+        } else {
+          cx = Math.round(cell.bbox_pct.x / 100 * imgW)
+          cy = Math.round(cell.bbox_pct.y / 100 * imgH)
+        }
         if (cw <= 0 || ch <= 0) continue
+        // Clamp to image bounds
+        if (cx < 0) cx = 0
+        if (cy < 0) cy = 0
+        if (cx + cw > imgW || cy + ch > imgH) continue
 
         const imageData = ctx.getImageData(cx, cy, cw, ch)
 
@@ -70,7 +97,7 @@ export function usePixelWordPositions(
         // Find dark-pixel clusters (word groups on the image)
         const threshold = Math.max(1, ch * 0.03)
         const minGap = Math.max(5, Math.round(cw * 0.02))
-        const clusters: { start: number; end: number }[] = []
+        let clusters: { start: number; end: number }[] = []
         let inCluster = false
         let clStart = 0
         let gap = 0
@@ -92,6 +119,15 @@ export function usePixelWordPositions(
 
         if (clusters.length === 0) continue
 
+        // When rotated 180°, mirror clusters back to original coordinate system
+        // A cluster at (start, end) in rotated space = (cw-1-end, cw-1-start) in original
+        if (rotation === 180) {
+          clusters = clusters.map(c => ({
+            start: cw - 1 - c.end,
+            end: cw - 1 - c.start,
+          })).reverse() // reverse to restore left-to-right order in original space
+        }
+
         const wordPos: WordPosition[] = []
 
         if (groups.length <= 1) {
@@ -156,7 +192,7 @@ export function usePixelWordPositions(
       setCellWordPositions(positions)
     }
     img.src = imageUrl
-  }, [active, cells, imageUrl])
+  }, [active, cells, imageUrl, rotation])
 
   return cellWordPositions
 }