Internal model test routes fetched 127.0.0.1:UPDATER_CONFIG.appPort
(hardcoded 20128). When PORT env is set to a different value, the app
listens on PORT but the internal fetch still targets 20128, causing
"fetch failed" on /api/models/test and /api/providers/[id]/test-models.
Fall back to UPDATER_CONFIG.appPort only when process.env.PORT is unset.