fix: swap 90°/270° rotation direction in orientation detection

Tesseract OSD 'rotate' returns the clockwise correction needed,
but the code was applying counterclockwise for 90° and clockwise
for 270° — exactly reversed. This caused pages scanned sideways
to be flipped upside down instead of corrected.

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

klausur-service/backend/cv_preprocessing.py

@@ -113,13 +113,13 @@ def detect_and_fix_orientation(img_bgr: np.ndarray) -> Tuple[np.ndarray, int]:
         if rotate == 0 or confidence < 1.0:
             return img_bgr, 0
 
-        # Apply rotation
+        # Apply rotation — OSD rotate is the clockwise correction needed
         if rotate == 180:
             corrected = cv2.rotate(img_bgr, cv2.ROTATE_180)
         elif rotate == 90:
-            corrected = cv2.rotate(img_bgr, cv2.ROTATE_90_COUNTERCLOCKWISE)
-        elif rotate == 270:
             corrected = cv2.rotate(img_bgr, cv2.ROTATE_90_CLOCKWISE)
+        elif rotate == 270:
+            corrected = cv2.rotate(img_bgr, cv2.ROTATE_90_COUNTERCLOCKWISE)
         else:
             return img_bgr, 0