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/Dockerfile

@@ -10,7 +10,7 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
 
 # PyTorch CPU-only — separate layer; the whl/cpu index strips all CUDA variants (~2 GB saved)
 RUN pip install --no-cache-dir \
-    torch==2.5.1 \
+    torch==2.7.1 \
     --index-url https://download.pytorch.org/whl/cpu
 
 COPY requirements.txt .