docs(env): justify the TRAE_WEB_ORIGIN allowlist entry (#12190)

scripts/check/check-env-doc-sync.mjs

@@ -283,6 +283,8 @@ const ENV_ONLY_ALLOWLIST = new Set([
   "PII_WINDOW_SIZE",
   "TRAE_STREAM_TIMEOUT_MS",
   "TRAE_TOKEN",
+  // #12190: Trae host/Origin override. ENVIRONMENT.md documents no Trae variable at
+  // all; this joins its two siblings above under the same .env.example-only tier.
   "TRAE_WEB_ORIGIN",
 ]);