Move healthcheck into Dockerfile and simplify docker-compose.yml

Uses BusyBox wget (included in Alpine) instead of Node.js fetch for the
health check. docker-compose.yml now references the published GHCR image
instead of building locally.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Dockerfile

@@ -37,5 +37,8 @@ USER nextjs
 EXPOSE 3000
 VOLUME /data
 
+HEALTHCHECK --interval=30s --timeout=10s --start-period=30s --retries=3 \
+  CMD wget -qO /dev/null http://localhost:3000/api/health
+
 ENTRYPOINT ["/sbin/tini", "--"]
 CMD ["node", "server.js"]