replace dead Tailwind classes in shop pages with custom CSS

Coming soon page was unstyled after Tailwind removal — replaced
utility classes with proper component CSS. Also removed dead h-full
classes from shop_root layout, adding height: 100% to the shop reset.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

lib/berrypod_web/live/shop/coming_soon.ex

@@ -9,10 +9,10 @@ defmodule BerrypodWeb.Shop.ComingSoon do
   @impl true
   def render(assigns) do
     ~H"""
-    <main class="flex min-h-screen items-center justify-center px-6 text-center" role="main">
+    <main class="coming-soon" role="main">
       <div>
-        <h1 class="text-3xl font-bold tracking-tight sm:text-4xl">{@theme_settings.site_name}</h1>
-        <p class="mt-4 text-lg text-[var(--t-text-muted)]">
+        <h1 class="coming-soon-title">{@theme_settings.site_name}</h1>
+        <p class="coming-soon-message">
           We're getting things ready. Check back soon.
         </p>
       </div>