fix(gateway): load dotenv before federation tier gate (#1138)

apps/gateway/src/app.module.ts

@@ -31,7 +31,9 @@ import { loadConfig } from '@mosaicstack/config';
 // Federation (step-ca client, enrollment, federation verbs) is only wired for
 // tier 'federated' — CaService hard-requires STEP_CA_* at construction, which
 // must not gate standalone/local boots (docker-compose.federated.yml: the
-// federation profile "must not start in non-federated dev").
+// federation profile "must not start in non-federated dev"). The gateway
+// entrypoint loads env.ts before evaluating this module so dotenv-backed tier
+// configuration is visible here.
 const federationEnabled = loadConfig().tier === 'federated';
 
 @Module({