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>

assets/css/admin/components.css

@@ -608,3 +608,12 @@
   &.active .admin-swap-on { display: inline-flex; }
   &.active .admin-swap-off { display: none; }
 }
+
+/* ── Theme toggle ── */
+
+.theme-toggle-indicator {
+  transition: left 150ms cubic-bezier(0.4, 0, 0.2, 1);
+}
+
+[data-theme="light"] .theme-toggle-indicator { left: 33.333333%; }
+[data-theme="dark"] .theme-toggle-indicator { left: 66.666667%; }