Add non-root user support and entrypoint script for Docker setup

Dockerfile

@@ -19,20 +19,23 @@ ENV NODE_ENV=production
 # DATA_DIR is the single volume mount point for both SQLite and uploads
 ENV DATA_DIR=/data
 
-# Create a non-root user
-RUN addgroup --system --gid 1001 nodejs && \
-    adduser --system --uid 1001 nextjs && \
+# Create a non-root user with default UID/GID (overridable at runtime via PUID/PGID)
+RUN apk add --no-cache su-exec shadow && \
+    addgroup --gid 1001 nodejs && \
+    adduser --uid 1001 --ingroup nodejs --disabled-password --gecos "" nextjs && \
     mkdir -p /data/uploads && chown -R nextjs:nodejs /data
 
 # Copy standalone build output
 COPY --from=builder --chown=nextjs:nodejs /app/.next/standalone ./
 COPY --from=builder --chown=nextjs:nodejs /app/.next/static ./.next/static
 COPY --from=builder --chown=nextjs:nodejs /app/public ./public
-
-USER nextjs
+COPY --chmod=755 entrypoint.sh /entrypoint.sh
 
 EXPOSE 3000
 ENV PORT=3000
 ENV HOSTNAME=0.0.0.0
+ENV PUID=1001
+ENV PGID=1001
 
+ENTRYPOINT ["/entrypoint.sh"]
 CMD ["node", "server.js"]