Fix port mismatch for Caddy reverse proxy

- Change application port from 3000 to 80
- Match Caddy's upstream proxy configuration
- Update healthcheck to use port 80
- Fix 502 gateway errors

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Dockerfile

@@ -36,12 +36,12 @@ RUN adduser -S nextjs -u 1001
 RUN chown -R nextjs:nodejs /app
 USER nextjs
 
-# Expose port 3000 (Coolify default)
-EXPOSE 3000
+# Expose port 80 (to match Caddy configuration)
+EXPOSE 80
 
 # Add healthcheck
 HEALTHCHECK --interval=30s --timeout=3s --start-period=5s --retries=3 \
-  CMD curl -f http://localhost:3000/ || exit 1
+  CMD curl -f http://localhost:80/ || exit 1
 
 # Start the server
-CMD ["serve", "-s", "dist", "-l", "3000"]
+CMD ["serve", "-s", "dist", "-l", "80"]