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/StepOrientation.tsx

@@ -30,14 +30,6 @@ export function StepOrientation({ sessionId: existingSessionId, onNext, onSubSes
   const [dragOver, setDragOver] = useState(false)
   const [sessionName, setSessionName] = useState('')
 
-  // Reset state when sessionId changes
-  useEffect(() => {
-    setSession(null)
-    setOrientationResult(null)
-    setPageSplitResult(null)
-    setError(null)
-  }, [existingSessionId])
-
   // Reload session data when navigating back
   useEffect(() => {
     if (!existingSessionId || session) return