feat: finalize file structure for Docker

docker/Dockerfile.planetgen

@@ -0,0 +1,17 @@
+FROM debian:12-slim
+ADD ./planetgen /opt/planetgen
+RUN <<EOF
+	set -e
+	export DEBIAN_FRONTEND=noninteractive
+	export DEBCONF_NONINTERACTIVE_SEEN=true
+	apt-get update && apt-get dist-upgrade -uy
+
+	apt-get install -y perl povray
+
+	mkdir -p /var/spool/pgen/{input,output}
+	chown -R www-data:www-data /var/spool/pgen
+EOF
+
+VOLUME /var/spool/pgen/input /var/spool/pgen/output
+
+ENTRYPOINT ["/opt/planetgen/planetmaker.pl"]