Host-local media sends were rejecting ZIP attachments with the error
'Host-local media sends only allow buffer-verified images, audio, video,
PDF, and Office documents (got application/zip)'.
This adds application/zip to the HOST_READ_ALLOWED_DOCUMENT_MIMES set,
enabling agents to send ZIP files via the message tool. ZIP files are
validated by file-type magic bytes detection, ensuring they are genuine
archives rather than disguised executables.
Fixes#78057 (regression from v2026.4.23 to v2026.5.2).