Feat/archive organizations

[Furan05]

Related issue(s)

Closes #938

How to test manually

1. Log in as a super-admin (e.g. "alix@example.com")
2. Go to an organization's settings page
3. Verify the new "Archive an organization" panel is visible between the
   edit form and the deletion panel
4. Submit the archive form with an optional deletion date and (optionally)
   a list of users to archive at the same time
5. Verify the organization is now displayed with a permanent banner
   indicating its archived status (and deletion date if set)
6. Verify any "manage" action (edit, delete tickets, contracts...) is now
   blocked on this organization, while "see" actions remain available
7. Verify archived users no longer appear in user lists and searches
8. Go back to the organizations page and verify the link
   "X archived organizations" is displayed
9. Click on the link and verify the archived organization is listed
10. Trigger the "CleanData" message (or wait for the cron) with a deletion
    date in the past to verify the organization is automatically deleted

To test as a non-super-admin, edit an agent role, check the new
"Archive the organization" permission, and assign that role to a user
on the target organization.

Reviewer checklist

• Code is manually tested
• Permissions / authorizations are verified
• New data can be imported
• Interface works on both mobiles and big screens
• Interface works in both light and dark modes
• Interface works on both Firefox and Chrome
• Accessibility has been tested
• Translations are synchronized
• Tests are up to date
• Copyright notices are up to date
• Documentation is up to date
• Pull request has been reviewed and approved

---

The super-admin bypass is in a separate commit
("feat: Allow super-admins to archive organizations without an agent role")
and can be reverted independently if you prefer to require an explicit
agent grant.