perf: split CSS bundles for shop and admin pages

Create separate CSS bundles to reduce shop page load times:
- app-shop.css (45KB/7.8KB gzip): Shop pages only, no daisyUI
- app.css (139KB): Admin pages with daisyUI and theme editor

Key changes:
- Add app-shop.css with targeted @source paths for shop files only
- Move .preview-frame rules from theme-layer2-attributes.css to app.css
- Delete fonts.css (fonts now generated inline by CSSGenerator)
- Add inline all-fonts generation in theme editor for typography switching
- Configure separate Tailwind profiles and watchers for both bundles

Shop pages now load 54% less CSS by excluding:
- daisyUI components (admin only)
- .preview-frame theme switching rules (editor only)
- Admin-specific Tailwind utilities

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

config/config.exs

@@ -63,6 +63,13 @@ config :tailwind,
       --output=priv/static/assets/css/app.css
     ),
     cd: Path.expand("..", __DIR__)
+  ],
+  simpleshop_theme_shop: [
+    args: ~w(
+      --input=assets/css/app-shop.css
+      --output=priv/static/assets/css/app-shop.css
+    ),
+    cd: Path.expand("..", __DIR__)
   ]
 
 # Configures Elixir's Logger