The mesh's own check caught it: an env-file-loaded secret still reaches
the process environment, readable via docker inspect and /proc (hq
04-ISSUES/041) -- the same class of exposure the file-based delivery
exists to avoid. Added MESH_NEXTCLOUD_ADMIN_PASSWORD_FILE support to the
client, matching the pattern the minio client already uses, and mounted
the sealed admin secret directly rather than writing it into an env-file.