DELETE /v1/files/{id} only lets a proxy admin key delete a raw s3:// or
gs:// file id, because such ids skip the managed-file owner check. The
batch lifecycle cleanup deleted the vertex_ai raw ids with the test's
own virtual key and got a 403 at teardown on every build since #194
Raw cloud-storage ids now go through the master key; managed and
provider-native ids keep using the creating key
