collaboration_attachment rows per record, uploads streamed into the
configured bucket with size limits and sha256, presigned downloads and
FILE_PREVIEW previews, a streamed-ETL Delete attachments action, parent
cleanup, the home card, and a parent-access stand-in for core's
record-reference security (QRun-IO/qqq#1138) to be replaced when released.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>