Sensible default colors

[yashranjan1]

We need to pick a set of sensible default themes so that the app works flawlessly on differently themed terminals that different people have. The idea is to add support for common themes (like ghostty does) and let the user pick what theme they want.

• A theme picker that allows people to pick preset default themes
• A config file that allows people to create their own themes
• Plan the colors for the statusline