The file browser/editor could only download individual files. Add a
recursive directory download that streams the folder as a zip archive,
on the local host and on every remote agent.
- file_service.archive_dir(): zip a directory recursively into a temp
file, preserving the folder name as the archive root and empty
subdirectories; symlinks are skipped (no sandbox escape / loops).
- /api/files/download and /agent/files/download branch on directories
and return application/zip, cleaning up the temp file afterwards.
- Files page: show the download button for folders too (as <name>.zip).
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>