feat: add shadcn/ui + Tailwind CSS v4 + Huge Icons foundation

- Install tailwindcss, @tailwindcss/postcss, clsx, tailwind-merge, class-variance-authority
- Install @hugeicons/react for icons
- Install Radix UI primitives (switch, tabs, label, separator, select, dialog, checkbox, dropdown-menu, popover)
- Install sonner for toast notifications
- Create postcss.config.js with Tailwind v4 PostCSS plugin
- Create jsconfig.json with @ path alias for src/admin
- Create components.json for shadcn configuration
- Update webpack.config.js with @ resolve alias
- Create globals.css with Tailwind v4 CSS-first config + shadcn CSS variables
- Create cn() utility in lib/utils.js
- Create 17 shadcn UI components (button, input, label, checkbox, switch, tabs, alert, separator, badge, textarea, dialog, sonner, table, skeleton, select, dropdown-menu, popover)
- Create async confirm() utility replacing SweetAlert2
- Create toast utility wrapping sonner

src/admin/components/ui/separator.js

@@ -0,0 +1,20 @@
+import * as SeparatorPrimitive from '@radix-ui/react-separator';
+import { cn } from '@/lib/utils';
+
+function Separator({ className, orientation = "horizontal", decorative = true, ...props }) {
+    return (
+        <SeparatorPrimitive.Root
+            data-slot="separator"
+            decorative={decorative}
+            orientation={orientation}
+            className={cn(
+                "shrink-0 bg-border",
+                orientation === "horizontal" ? "h-[1px] w-full" : "h-full w-[1px]",
+                className
+            )}
+            {...props}
+        />
+    );
+}
+
+export { Separator };