POST /video/import-drive {resourceId} pulls through the oCIS WebDAV
service-account client; POST /video/import-chat {mxcUri} pulls from the
Matrix content repository (MATRIX_MEDIA_TOKEN, homeserver falls back to
ARCHIVE_PROVISIONER_HOMESERVER_URL). Both cap at 256 MiB (buffered v1,
streaming follow-up), store through the same encrypted content-
addressed path as uploads, probe, and audit video.imported with
provenance.
