fix: einheitliche Schriftgroesse + Border-Cluster-Filter im Overlay

1. Schriftgroesse basiert jetzt auf Median-Zeilenhoehe statt
   individueller Zellhoehe — keine Groessensprunge in Box-Bereichen
2. Sehr schmale Pixel-Cluster (< 0.5% Zellbreite) werden gefiltert,
   damit Box-Rahmen nicht als Textposition erkannt werden

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

admin-lehrer/components/ocr-overlay/OverlayReconstruction.tsx

@@ -316,6 +316,14 @@ export function OverlayReconstruction({ sessionId, onNext }: OverlayReconstructi
   const imgH = imageNaturalSize?.h || 1
   const containerH = reconWidth * (imgH / imgW)
 
+  // Compute median cell height (in px) for consistent font sizing
+  const medianCellHeightPx = useMemo(() => {
+    if (cells.length === 0) return 40
+    const heights = cells.map(c => containerH * (c.bboxPct.h / 100)).sort((a, b) => a - b)
+    const mid = Math.floor(heights.length / 2)
+    return heights.length % 2 === 0 ? (heights[mid - 1] + heights[mid]) / 2 : heights[mid]
+  }, [cells, containerH])
+
   return (
     <div className="space-y-3">
       {/* Toolbar */}
@@ -460,13 +468,12 @@ export function OverlayReconstruction({ sessionId, onNext }: OverlayReconstructi
               const edited = isEdited(cell)
               const wordPos = cellWordPositions.get(cell.cellId)
               const bboxPct = cell.bboxPct
-              const cellHeightPx = containerH * (bboxPct.h / 100)
               const colorValue = textColor === 'black' ? '#1a1a1a' : textColor
 
               // Pixel-analysed: render word-groups at detected positions
               if (wordPos && wordPos.length > 0) {
                 return wordPos.map((wp, i) => {
-                  const autoFontPx = cellHeightPx * wp.fontRatio * fontScale
+                  const autoFontPx = medianCellHeightPx * wp.fontRatio * fontScale
                   const fs = Math.max(6, autoFontPx)
 
                   if (wordPos.length > 1) {
@@ -536,7 +543,7 @@ export function OverlayReconstruction({ sessionId, onNext }: OverlayReconstructi
               // Fallback: no pixel data — single input at cell bbox
               if (!cell.text) return null
 
-              const fontSize = Math.max(6, cellHeightPx * fontScale)
+              const fontSize = Math.max(6, medianCellHeightPx * fontScale)
               return (
                 <div key={cell.cellId} className="absolute group" style={{
                   left: `${bboxPct.x}%`,

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

@@ -112,6 +112,11 @@ export function usePixelWordPositions(
 
         if (clusters.length === 0) continue
 
+        // Filter out very narrow clusters (likely box borders / vertical lines)
+        const minClusterW = Math.max(3, Math.round(cw * 0.005))
+        clusters = clusters.filter(c => (c.end - c.start + 1) > minClusterW)
+        if (clusters.length === 0) continue
+
         if (rotation === 180) {
           clusters = clusters.map(c => ({
             start: cw - 1 - c.end,