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/reset.css

@@ -0,0 +1,19 @@
+/* Minimal resets for admin pages */
+
+*, *::before, *::after {
+  box-sizing: border-box;
+}
+
+body {
+  margin: 0;
+}
+
+/* Make LiveView wrapper divs transparent for layout */
+[data-phx-session], [data-phx-teleported-src] {
+  display: contents;
+}
+
+/* Phoenix LiveView loading states */
+.phx-no-feedback.phx-no-feedback {
+  /* Suppress validation styles until form is interacted with */
+}