Archive links in the archive list open a new tab instead of downloading the file

Problem/Motivation

The links in the File column of the archive list (/admin/content/earkiv) do not download the archive. In Chrome the link opens a new tab instead.

The file entity of the archive is created without a MIME type, so filemime is empty in file_managed. The response for the private file then has no Content-Type header and no Content-Disposition header, and the browser has to guess what to do with a file of several gigabytes.

Steps to reproduce

1. Create and store an archive.
2. Go to /admin/content/earkiv and click the file name.
3. Chrome opens a new tab instead of downloading the file. curl -I on the file URL shows no Content-Type.

Proposed resolution

• Set the MIME type application/gzip when the file entity of the archive is created.
• Add the download attribute to the link in the archive list, so the browser saves the file instead of opening it.
• Add a post update function that sets the MIME type of the existing archive files.

Remaining tasks

• Implement and test.
• Review.

User interface changes

Clicking an archive in the list downloads it.

API changes

None.

Data model changes

None. A post update function sets filemime for existing archive files.

AI-Generated: Yes (Used Claude Code to find the cause and draft this issue.)