fix(ocr): add pyvips for kraken PDF input support

Kraken 7 requires pyvips (optional dep) for -f pdf mode.
Added libvips42 system package and pyvips Python package.

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

ocr-service/Dockerfile

@@ -2,10 +2,11 @@ FROM python:3.11-slim
 
 WORKDIR /app
 
-# curl for healthcheck; libgomp1 for PyTorch CPU threading
+# curl for healthcheck; libgomp1 for PyTorch CPU threading; libvips for kraken PDF support
 RUN apt-get update && apt-get install -y --no-install-recommends \
     curl \
     libgomp1 \
+    libvips42 \
     && rm -rf /var/lib/apt/lists/*
 
 # PyTorch CPU-only — separate layer; the whl/cpu index strips all CUDA variants (~2 GB saved)

ocr-service/requirements.txt

@@ -6,4 +6,5 @@ torchvision==0.22.1
 transformers>=4.56.1,<5.0.0
 pillow>=10.2.0,<11.0.0
 pypdfium2==4.30.0
+pyvips>=2.2.0
 httpx==0.28.1