mobile quarantine: add dark theme support to the mobile quarantine

mobile quarantine: add dark theme support to the mobile quarantine

enable the `autoDarkTheme` option for the mobile quarantine and add
minimal styling to correct the look of the logo and the mail preview
rendering. this makes the quarantine behave like the "auto" theme of
the main gui, it will change it's theme depending on a media query.

Signed-off-by: Stefan Sterz <s.sterz@proxmox.com>
Reviewed-by: Dominik Csapak <d.csapak@proxmox.com>
Tested-by:  Dominik Csapak <d.csapak@proxmox.com>