feat(actions): bulk delete, disable and enable runners in admin UI (#37869)

Adds bulk actions on the site-admin runner list
(`/-/admin/actions/runners`). Site admins can now select multiple
runners and **Delete**, **Disable**, or **Enable** them in one go
instead of clicking through each runner's edit page.

Scope is intentionally limited to the admin page. The user, org, and
repo runner pages keep their existing per-row UX — the shared list
template gates the bulk UI behind an `AllowBulkActions` flag set only by
the admin handler.

## Screenshots

<img width="1582" height="353"
src="https://github.com/user-attachments/assets/2125661f-aac0-4168-990a-97995a26abd2"
/>

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Signed-off-by: Nicolas <bircni@icloud.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>