fix: add data attributes and Google Fonts to enable theme visual changes

- Add Google Fonts link to root layout for typography presets
- Add data-mood, data-typography, data-shape, data-density attributes to preview-frame
- Create theme-layer2-attributes.css with attribute-based CSS from demo
- Move theme CSS files from priv/static/css to assets/css for proper compilation
- Update CSS import order (primitives → layer2 → semantic)
- Add 'css' to static_paths to serve theme CSS files

This fixes the issue where theme controls updated the database but didn't
visually affect the preview. The demo's attribute-based CSS system is now
properly integrated with the Phoenix LiveView implementation.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

lib/simpleshop_theme_web/components/layouts/root.html.heex

@@ -8,6 +8,9 @@
       {assigns[:page_title]}
     </.live_title>
     <link phx-track-static rel="stylesheet" href={~p"/assets/css/app.css"} />
+    <link rel="preconnect" href="https://fonts.googleapis.com">
+    <link rel="preconnect" href="https://fonts.gstatic.com" crossorigin>
+    <link href="https://fonts.googleapis.com/css2?family=Fraunces:opsz,wght@9..144,400;9..144,500;9..144,600;9..144,700&family=Inter:wght@400;500;600;700&family=Libre+Baskerville:wght@400;700&family=Nunito:wght@400;600;700&family=Nunito+Sans:opsz,wght@6..12,300;6..12,400;6..12,500;6..12,600&family=Outfit:wght@300;400;500;600&family=Source+Sans+3:wght@400;500;600&family=Space+Grotesk:wght@400;500;600&display=swap" rel="stylesheet">
     <script defer phx-track-static type="text/javascript" src={~p"/assets/js/app.js"}>
     </script>
     <script>