ayu palette and file icons

• Colors follow the current ayu palette, shared with ayu for VS Code. Light changes the most
• ayu's own file icons, the same set as VS Code, now cover 142 file types through A File Icon
• Separators between panels are shown by default. Set "ui_separator": false to hide them
• The command palette input blends into the palette instead of standing out
• Zig storage types are colored as types