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>

lib/simpleshop_theme_web/live/theme_live/index.html.heex

@@ -938,6 +938,11 @@
              data-shadow={@theme_settings.card_shadow}
              data-button-style={@theme_settings.button_style}>
           <style>
+            /* All font faces for theme switching */
+            <%= Phoenix.HTML.raw(SimpleshopTheme.Theme.Fonts.generate_all_font_faces(
+                  &SimpleshopThemeWeb.Endpoint.static_path/1
+                )) %>
+            /* Generated theme CSS */
             <%= Phoenix.HTML.raw(@generated_css) %>
           </style>