Nextcloud 30 UI refresh

[marcoambrosini]

Efforts to streamline and refresh the user interface for Nextcloud 30

• Reduce border radius
  Reduce border radius of components nextcloud-libraries/nextcloud-vue#5483
  Reduce app container border radius #44786
• Input elements with 1 px border
• Make the interface more compact #45657
• New Backgrounds feat(theming): Allow shipped backgrounds to have a dark variant #46453
• Sidebar's animation

[marcoambrosini]

done