Logo is invisible on the login page #3772

Describe the bug

The logo on the login page is invisible with the default theme. The login page uses common.logo from the theme (themes/opencloud/assets/logo.svg), which is dark petrol (#20434F) since #2599, on the dark petrol login background (#20434F).

Steps to reproduce

1. Start OpenCloud with the default theme.
2. Open the login page.

Expected behavior

The logo is visible, as before 7.3.0.

Actual behavior

The logo is there but has the same colour as the background.

Setup

Default opencloud theme, no IDP_LOGIN_BACKGROUND_URL.

Additional context

logo.svg is also the web app's light theme logo (clients.web.defaults.logo), so common.logo should point to the lilac logo instead.