fix: Use correct NestJS output directory (dist_user)

- NestJS is configured to build to dist_user in nest-cli.json
- Copy from /app/dist_user instead of /app/dist

Author: rizrmd

Dockerfile

@@ -120,7 +120,7 @@ COPY --from=backend-deps --chown=nodejs:nodejs /app/prisma ./prisma
 
 # Copy backend package files and built source
 COPY --chown=nodejs:nodejs backend/package*.json ./
-COPY --from=backend-deps --chown=nodejs:nodejs /app/dist ./dist
+COPY --from=backend-deps --chown=nodejs:nodejs /app/dist_user ./dist
 COPY --chown=nodejs:nodejs backend/src ./src
 
 # Copy Next.js standalone build