fix: replace reset useEffects with key prop for step component remount

The reset useEffects in StepOrientation/Deskew/Dewarp/Crop were clearing
orientationResult when sessionId changed (e.g. during handleOrientationComplete),
causing the right side of ImageCompareView to show nothing. Using key={sessionId}
on the step components instead forces React to remount with fresh state when
switching sessions, without interfering with the upload/orientation flow.

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

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

@@ -17,13 +17,6 @@ export function StepCrop({ sessionId, onNext }: StepCropProps) {
   const [error, setError] = useState<string | null>(null)
   const [hasRun, setHasRun] = useState(false)
 
-  // Reset state when sessionId changes (e.g. switching sub-sessions)
-  useEffect(() => {
-    setCropResult(null)
-    setHasRun(false)
-    setError(null)
-  }, [sessionId])
-
   // Auto-trigger crop on mount
   useEffect(() => {
     if (!sessionId || hasRun) return