Fix Docker volume permissions for backend runtime

backend/Dockerfile

@@ -5,16 +5,18 @@ ENV NODE_ENV=production
 WORKDIR /app
 
 COPY package*.json ./
-RUN apk add --no-cache curl && npm install --omit=dev
+RUN apk add --no-cache curl su-exec && npm install --omit=dev
 
 COPY . .
 RUN chown -R node:node /app
 
-USER node
+COPY docker-entrypoint.sh /usr/local/bin/docker-entrypoint.sh
+RUN chmod +x /usr/local/bin/docker-entrypoint.sh
 
 EXPOSE 4000
 
 HEALTHCHECK --interval=30s --timeout=5s --start-period=5s --retries=3 \
 	CMD curl -f http://localhost:4000/health || exit 1
 
+ENTRYPOINT ["docker-entrypoint.sh"]
 CMD ["node", "index.js"]

backend/docker-entrypoint.sh

@@ -0,0 +1,7 @@
+#!/bin/sh
+set -eu
+
+mkdir -p /app/data /app/uploads
+chown -R node:node /app/data /app/uploads
+
+exec su-exec node "$@"