fix: resolve volume permission error for non-root container user

Entrypoint now runs as root, chowns the data directory to appuser,
then drops privileges via gosu before starting Gunicorn. This prevents
sqlite3.OperationalError on mounted volumes owned by root.

Dockerfile

@@ -4,8 +4,8 @@ FROM python:3.9-slim
 # Set the working directory
 WORKDIR /app
 
-# Install system dependencies (including gettext for envsubst)
-RUN apt-get update && apt-get install -y gettext && rm -rf /var/lib/apt/lists/*
+# Install system dependencies (including gettext for envsubst and gosu for privilege dropping)
+RUN apt-get update && apt-get install -y gettext gosu && rm -rf /var/lib/apt/lists/*
 
 # Install Python dependencies
 COPY requirements.txt .
@@ -30,7 +30,7 @@ ARG UID=1000
 ARG GID=1000
 RUN groupadd -g ${GID} appuser && useradd -u ${UID} -g ${GID} -s /bin/sh -M appuser
 RUN chown -R appuser:appuser /app /entrypoint.sh
-USER appuser
+# Entrypoint runs as root, fixes volume permissions, then drops to appuser via gosu
 
 # Use the entrypoint script as the container's command
 CMD ["/entrypoint.sh"]