fix: add libcairo2-dev and pkg-config for pycairo/svglib/xhtml2pdf build

Dockerfile

@@ -1,10 +1,16 @@
 FROM python:3.12-slim
 
-# System deps: pg_isready (postgresql-client) + build tools for psycopg2
+# System deps:
+#   postgresql-client  - pg_isready in entrypoint
+#   gcc, libpq-dev     - psycopg2 build
+#   libcairo2-dev      - pycairo (required by svglib -> xhtml2pdf)
+#   pkg-config         - required by pycairo's meson build
 RUN apt-get update && apt-get install -y --no-install-recommends \
     postgresql-client \
     gcc \
     libpq-dev \
+    libcairo2-dev \
+    pkg-config \
     && rm -rf /var/lib/apt/lists/*
 
 WORKDIR /app