8-color/3-bit fallback (for tty)

[MithicSpirit]

Is your feature request related to a problem? Please describe.
Using the catppuccin theme makes neovim terrible to use in a regular TTY, since everything is black and white.

Describe the solution you'd like
I think that it would be helpful to provide an 8-color/3-bit fallback for such situations so that it's still usable, even if it doesn't look as good as the normal theme.

Describe alternatives you've considered
I could also conditionally set up catppuccin or another theme, depending on my terminal's capabilities.

[vollowx]

Try the following code snippet, since the default colorscheme supports TTY best.

-- At where you set the colorscheme

vim.g.has_ui = #vim.api.nvim_list_uis() > 0
vim.g.has_gui = vim.g.has_ui and (vim.env.DISPLAY ~= nil or vim.env.WAYLAND_DISPLAY ~= nil)

if not vim.g.has_gui then
  if vim.g.has_ui then
    vim.cmd.colorscheme('default')
  end
  return
end

vim.cmd.colorscheme({
  args = { 'catppuccin' },
  mods = { emsg_silent = true },
})