Use your own color within clients

[tobiasKaminsky]

Starting with NC25 user can choose a wallpaper and server generates a fitting color. We want to use this color also on clients.

• [ ] Server: expose color https://github.com/nextcloud/server/issues/35847
• [ ] Client:
  • [ ] use this new property in Capability
  • [ ] fallback to primary color as it is currently the case (e.g. <NC24, or when admin disabled it, or none is set)
  • [ ] Android: check that color is matching, as M3 uses "source" color to generate matching colors