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>

test/simpleshop_theme_web/live/theme_css_consistency_test.exs

@@ -5,9 +5,9 @@ defmodule SimpleshopThemeWeb.ThemeCSSConsistencyTest do
 
   Architecture:
   - Both shop pages and preview use .themed class for shared styles
-  - Theme editor uses .preview-frame[data-*] selectors for live switching
-  - Shop pages get theme values via inline CSS from CSSGenerator
-  - Component styles use .themed for shared styling
+  - Theme editor uses .preview-frame[data-*] selectors for live switching (in app.css)
+  - Shop pages get theme values via inline CSS from CSSGenerator (app-shop.css)
+  - Component styles use .themed for shared styling (theme-layer2-attributes.css)
   """
 
   use SimpleshopThemeWeb.ConnCase, async: false
@@ -88,12 +88,13 @@ defmodule SimpleshopThemeWeb.ThemeCSSConsistencyTest do
   end
 
   describe "CSS file structure" do
-    test "theme-layer2-attributes.css has .preview-frame variant selectors for editor" do
-      css_path = Path.join([File.cwd!(), "assets", "css", "theme-layer2-attributes.css"])
+    test "app.css has .preview-frame variant selectors for theme editor" do
+      css_path = Path.join([File.cwd!(), "assets", "css", "app.css"])
       css_content = File.read!(css_path)
 
       # Variant selectors are editor-only (.preview-frame) using CSS nesting
       # The file uses &[data-*] syntax inside .preview-frame { }
+      # These rules are in app.css (admin only), not app-shop.css
       assert css_content =~ ".preview-frame"
       assert css_content =~ "&[data-mood=\"dark\"]"
       assert css_content =~ "&[data-mood=\"warm\"]"