fix(tailwindcss): remove @source directive from css file

[andyl]

The line @source './site.css'; in site.css caused Tailwind to generate invalid CSS, breaking styling completely.

(ubuntu 22.04 / tailwind 4.10.0 / tableau_new 1.5.0)

To generate the Tableau site: mix tableau.new mysite --template heex --assets tailwind

My styling test case, from lib/pages/home_page.ex:

  def template(assigns) do
    ~H"""
    <p class="bg-amber-300">
      hello, world!
    </p>
    """
  end

After removing the line in site.css, the styling with Tailwind4 is working.

[mhanberg]

I confirmed this didn't work before and that this fixes it, but I don't believe its a v4 problem. I think the combination of using this @source directive and it using the standalone tailwind cli is having a weird problem.

But also, this directive isn't necessary. I copied it out of my blog, but I don't think I needed it.