fix(ocr): upgrade kraken to 6.0.3 for torch>=2.4 compatibility

kraken 5.2.9 required torch~=2.1.0, incompatible with surya-ocr's
torch>=2.3.0. kraken 6.0.3 requires torch>=2.4.0,<=2.9 which
overlaps with surya and our pinned torch==2.5.1.

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==5.2.9
+kraken==6.0.3
 pillow>=10.2.0,<11.0.0
 pypdfium2==4.30.0
 httpx==0.28.1