fix: fix SQLite database permission error on volume mounts

Entrypoint now runs as root, fixes ownership of /app/data to nextjs:nodejs
(uid 1001), then drops privileges via su before starting the app.
This fixes 'unable to open database file' when the host data/ directory
is created by Docker as root and is not writable by the nextjs user.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

backend/Dockerfile

@@ -32,7 +32,6 @@ COPY --from=builder /app/docker-entrypoint.sh ./
 RUN chmod +x docker-entrypoint.sh
 RUN mkdir -p /app/data && chown -R nextjs:nodejs /app/data
 
-USER nextjs
 EXPOSE 3000
 ENV PORT=3000
 ENV HOSTNAME=0.0.0.0

backend/docker-entrypoint.sh

@@ -1,4 +1,5 @@
 #!/bin/sh
 set -e
 mkdir -p /app/data
-exec node server.js
+chown -R 1001:1001 /app/data
+exec su -c "exec node server.js" nextjs