Name and timestamp in chat window not legible on dark desktop themes

**Describe the bug**

Name and timestamp in chat window not legible with dark desktop themes.

**To Reproduce**

Switch your system settings to use a dark theme and see the names in the chat mostly disappear.

**Expected behavior**

Use a different palette for dark desktop themes.

**Operating system**
All, because the colours are hardcoded at the server which doesn't know about the client's desktop colour scheme

**Version of Jamulus**

All

Reproduce the issue by switching the desktop to a dark theme and opening the chat window. Locate the chat name and timestamp rendering and its palette handling, then verify that both remain legible across light and dark desktop themes.

Written by the indexing model from the issue text.