fix: PaddleOCR CPU crash, content-aware-resize limits, barcode fixtures

- Add enable_mkldnn=False to PaddleOCR constructor to bypass PaddlePaddle
  3.3+ OneDNN/PIR crash on CPU-only systems
- Add 25MP and 75% max-reduction guard to seam carving with clear error
  messages instead of silent timeout/crash
- Replace barcode/QR AVIF test fixtures with actual scannable codes
  (old fixtures did not contain real barcodes)

packages/ai/python/ocr.py

@@ -143,6 +143,7 @@ def run_paddleocr_v5(input_path, language):
             lang=paddle_lang,
             device=device,
             ocr_version="PP-OCRv5",
+            enable_mkldnn=False,
         )
         emit_progress(30, "Scanning")
         results = ocr.predict(input=input_path)