fix: Paddle Direct keeps preprocessing (orient/deskew/dewarp/crop)

Uses the cropped/dewarped image instead of the original so the overlay
shows the correctly oriented page. 5 steps instead of 2.

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

klausur-service/backend/ocr_pipeline_api.py

@@ -2511,17 +2511,23 @@ async def _word_stream_generator(
 
 @router.post("/sessions/{session_id}/paddle-direct")
 async def paddle_direct(session_id: str):
-    """Run PaddleOCR on the original image and build a word grid directly.
+    """Run PaddleOCR on the preprocessed image and build a word grid directly.
 
-    Skips deskew/dewarp/crop/rows — just Upload → PaddleOCR → Overlay.
-    The original image is stored as cropped_png so OverlayReconstruction
+    Expects orientation/deskew/dewarp/crop to be done already.
+    Uses the cropped image (falls back to dewarped, then original).
+    The used image is stored as cropped_png so OverlayReconstruction
     can display it as the background.
     """
-    original_png = await get_session_image(session_id, "original")
-    if not original_png:
-        raise HTTPException(status_code=404, detail="No original image found for this session")
+    # Try preprocessed images first (crop > dewarp > original)
+    img_png = await get_session_image(session_id, "cropped")
+    if not img_png:
+        img_png = await get_session_image(session_id, "dewarped")
+    if not img_png:
+        img_png = await get_session_image(session_id, "original")
+    if not img_png:
+        raise HTTPException(status_code=404, detail="No image found for this session")
 
-    img_arr = np.frombuffer(original_png, dtype=np.uint8)
+    img_arr = np.frombuffer(img_png, dtype=np.uint8)
     img_bgr = cv2.imdecode(img_arr, cv2.IMREAD_COLOR)
     if img_bgr is None:
         raise HTTPException(status_code=400, detail="Failed to decode original image")
@@ -2562,11 +2568,11 @@ async def paddle_direct(session_id: str):
         },
     }
 
-    # Store original image as cropped_png so OverlayReconstruction shows it
+    # Store preprocessed image as cropped_png so OverlayReconstruction shows it
     await update_session_db(
         session_id,
         word_result=word_result,
-        cropped_png=original_png,
+        cropped_png=img_png,
         current_step=8,
     )