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>

assets/css/shop/reset.css

@@ -13,12 +13,14 @@
   }
 
   html {
+    height: 100%;
     -webkit-text-size-adjust: 100%;
     -moz-text-size-adjust: 100%;
     text-size-adjust: 100%;
   }
 
   body {
+    height: 100%;
     line-height: 1.5;
     -webkit-font-smoothing: antialiased;
   }
@@ -78,6 +80,11 @@
     cursor: pointer;
   }
 
+  /* Full-height shop root */
+  .shop-root {
+    height: 100%;
+  }
+
   /* LiveView wrapper divs are layout-invisible */
   [data-phx-session],
   [data-phx-teleported-src] {