feat(ocr): bump to latest surya 0.17.1, kraken 7.0, torch 2.7.1

- surya-ocr 0.6.3 → 0.17.1: new predictor API (FoundationPredictor,
  RecognitionPredictor, DetectionPredictor), native polygon output
  on text lines (4-point clockwise)
- kraken 5.2.9 → 7.0: wider torch range (>=2.4,<=2.10), unpinned numpy
- torch 2.5.1 → 2.7.1: satisfies surya's >=2.7.0 requirement
- Rewrite engines/surya.py for the 0.17 predictor class API
- Surya now outputs polygons natively — no longer rectangle-only

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

ocr-service/requirements.txt

@@ -1,6 +1,6 @@
 fastapi[standard]==0.115.6
-surya-ocr==0.6.3
-kraken==6.0.3
+surya-ocr==0.17.1
+kraken==7.0
 pillow>=10.2.0,<11.0.0
 pypdfium2==4.30.0
 httpx==0.28.1