fix: polish split-port implementation for merge

- Add 30s timeout to API bridge proxy requests to prevent resource exhaustion
- Extract healthcheck.mjs script (replaces inline node -e in Dockerfile + compose files)
- Add unit tests for runtime port resolution (14 tests, parsePort + resolveRuntimePorts)
- Fix formatting in declare global block

docker-compose.prod.yml

@@ -34,13 +34,7 @@ services:
     volumes:
       - omniroute-prod-data:/app/data
     healthcheck:
-      test:
-        [
-          "CMD",
-          "node",
-          "-e",
-          "const p=process.env.DASHBOARD_PORT||process.env.PORT||'20128';fetch('http://127.0.0.1:'+p+'/api/settings').then(r=>{if(!r.ok)throw r.status}).catch(()=>process.exit(1))",
-        ]
+      test: ["CMD", "node", "healthcheck.mjs"]
       interval: 30s
       timeout: 5s
       retries: 3