Background color of project home is auto-picked from the project avatar

Crazy idea: color the project homepage with the most dominant color in the avatar and also apply it to the header in a darker shade. When there’s no project avatar, we can have a neutral background (gray or that picks from the current theme). In the example image below, the project header background has a 40% black overlay and the nav/header has a 60% black overlay to tone down more vibrant colors.

Issues to solve

• The nav/header looks a bit weird over the sidebar nav, but I wasn’t sure how to make it look better.
• Needs some work to ensure the text meets a11y standards for contrast.
• Not sure how this ties in with the user's theme preference — does it override the theme?