fix(dev): proxy local API and restrict frontend upstream

docker/frontend-entrypoint.sh

@@ -3,13 +3,10 @@ set -eu
 
 THT_FRONTEND_API_UPSTREAM=${THT_FRONTEND_API_UPSTREAM:-http://core:8787}
 THT_FRONTEND_API_UPSTREAM=${THT_FRONTEND_API_UPSTREAM%/}
-case "$THT_FRONTEND_API_UPSTREAM" in
-  http://*|https://*) ;;
-  *)
-    echo "Invalid THT_FRONTEND_API_UPSTREAM: use an internal http(s) upstream" >&2
-    exit 2
-    ;;
-esac
+if ! /usr/local/bin/validate-frontend-api-upstream "$THT_FRONTEND_API_UPSTREAM"; then
+  echo "Invalid THT_FRONTEND_API_UPSTREAM: expected internal http://core:8787" >&2
+  exit 2
+fi
 export THT_FRONTEND_API_UPSTREAM
 
 if ! envsubst '${THT_FRONTEND_API_UPSTREAM}' \