Add repository tally to sidebar

[bennekrouf]

What changed

• Added a repository tally to the sidebar, displaying the count of repositories that need attention.
• Updated the CSS to style the tally element.
• Implemented the Tally struct and tally function to calculate the number of repositories that are live, have left a failure, or have a worth-saying want.
• Updated the RepoSidebar component to include the tally display.

Why

This feature provides a quick overview of the repository status, helping users to identify which repositories require their attention.

How to test

1. Open the application and navigate to the repository list screen.
2. Observe the sidebar to see the tally of repositories that need attention.
3. Check the tally updates correctly when you interact with different repositories, such as marking them as read or encountering failures.
4. Ensure the green tick appears when all repositories are clean and have been read at least once.