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/StepDewarp.tsx

@@ -20,13 +20,6 @@ export function StepDewarp({ sessionId, onNext }: StepDewarpProps) {
   const [showGrid, setShowGrid] = useState(true)
   const [error, setError] = useState<string | null>(null)
 
-  // Reset state when sessionId changes (e.g. switching sub-sessions)
-  useEffect(() => {
-    setDewarpResult(null)
-    setDeskewResult(null)
-    setError(null)
-  }, [sessionId])
-
   // Load session info to get deskew_result (for fine-tuning init values)
   useEffect(() => {
     if (!sessionId) return