Update Dockerfile

Dockerfile

@@ -1,12 +1,12 @@
-# Use the official Python image (non-slim to include full libraries)
-FROM python:3.9
+# Use a Debian-based Python image for reliable package installation
+FROM python:3.9-buster
 
-# Prevent Python from writing .pyc files and enable unbuffered output
+# Prevent Python from writing pyc files and enable unbuffered output
 ENV PYTHONDONTWRITEBYTECODE=1
 ENV PYTHONUNBUFFERED=1
 
 # Update package lists and install system dependencies:
-# - graphviz (for the dot executable)
+# - graphviz (provides the dot executable)
 # - wkhtmltopdf (for PDF generation)
 RUN apt-get update && apt-get install -y \
     graphviz \
@@ -19,7 +19,6 @@ RUN apt-get update && apt-get install -y \
 ENV PATH="/usr/local/bin:${PATH}"
 ENV GRAPHVIZ_DOT="/usr/local/bin/dot"
 
-# Set working directory
 WORKDIR /app
 
 # Copy and install Python dependencies