fix(ocr): pin transformers<5.0 and torch==2.7.1 in requirements.txt

transformers 5.x breaks surya 0.17.1 — SuryaDecoderConfig is missing
pad_token_id. Pin to transformers>=4.56.1,<5.0.0.

Also add torch==2.7.1 to requirements.txt to prevent pip from upgrading
it past the CPU-only build installed in the Dockerfile layer.

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

ocr-service/requirements.txt

@@ -1,6 +1,8 @@
 fastapi[standard]==0.115.6
 surya-ocr==0.17.1
 kraken==7.0
+torch==2.7.1
+transformers>=4.56.1,<5.0.0
 pillow>=10.2.0,<11.0.0
 pypdfium2==4.30.0
 httpx==0.28.1