fix: add error handling and logging to OCR endpoint

Return detailed error message instead of generic 500, and handle
empty OCR results gracefully.

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

paddleocr-service/main.py

@@ -88,10 +88,17 @@ async def ocr(
     img = Image.open(io.BytesIO(img_bytes)).convert("RGB")
     img_np = np.array(img)
 
+    try:
         result = _engine.ocr(img_np)
+    except Exception as e:
+        logger.error(f"OCR failed: {e}", exc_info=True)
+        raise HTTPException(status_code=500, detail=f"OCR processing failed: {e}")
+
+    if not result or not result[0]:
+        return {"words": [], "image_width": img_np.shape[1], "image_height": img_np.shape[0]}
 
     words = []
-    for line in result[0] or []:
+    for line in result[0]:
         box, (text, conf) = line[0], line[1]
         x_min = min(p[0] for p in box)
         y_min = min(p[1] for p in box)