remove Tailwind + DaisyUI theme + heroicons plugin, admin fully custom CSS (Phase 7)

replace Tailwind CLI with esbuild for admin CSS bundling. admin now uses
hand-written utility classes (admin/utilities.css), static heroicon CSS
generated by mix generate_admin_icons, plain CSS colour themes extracted
from DaisyUI plugin config, and minimal resets. rename app.css to admin.css
for clarity alongside shop.css. delete vendor/daisyui-theme.js and
vendor/heroicons.js. no Tailwind dependency remains in the project.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

test/simpleshop_theme_web/live/theme_css_consistency_test.exs

@@ -5,8 +5,8 @@ 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 (in app.css)
-  - Shop pages get theme values via inline CSS from CSSGenerator (app-shop.css)
+  - Theme editor uses .preview-frame[data-*] selectors for live switching (in admin.css)
+  - Shop pages get theme values via inline CSS from CSSGenerator (shop.css)
   - Component styles use .themed for shared styling (theme-layer2-attributes.css)
   """
 
@@ -90,13 +90,13 @@ defmodule SimpleshopThemeWeb.ThemeCSSConsistencyTest do
   end
 
   describe "CSS file structure" do
-    test "app.css has .preview-frame variant selectors for theme editor" do
-      css_path = Path.join([File.cwd!(), "assets", "css", "app.css"])
+    test "admin.css has .preview-frame variant selectors for theme editor" do
+      css_path = Path.join([File.cwd!(), "assets", "css", "admin.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
+      # These rules are in admin.css (admin only), not shop.css
       assert css_content =~ ".preview-frame"
       assert css_content =~ "&[data-mood=\"dark\"]"
       assert css_content =~ "&[data-mood=\"warm\"]"