fix: use node fetch for frontend health check

wget in node:22-alpine can't connect to localhost:3000 — use
node's built-in fetch instead, which works correctly.

docker-compose.yml

@@ -24,7 +24,7 @@ services:
     environment:
       - API_URL=http://backend:8080
     healthcheck:
-      test: ["CMD", "wget", "--spider", "-q", "http://localhost:3000"]
+      test: ["CMD", "node", "-e", "fetch('http://localhost:3000').then(r=>{if(!r.ok)throw r.status;process.exit(0)}).catch(()=>process.exit(1))"]
       interval: 30s
       timeout: 5s
       retries: 3