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/input.js

@@ -0,0 +1,17 @@
+import { cn } from '@/lib/utils';
+
+function Input({ className, type, ...props }) {
+    return (
+        <input
+            type={type}
+            data-slot="input"
+            className={cn(
+                "flex h-9 w-full rounded-[30px] border border-input bg-transparent px-3 py-1 text-sm shadow-sm transition-colors file:border-0 file:bg-transparent file:text-sm file:font-medium file:text-foreground placeholder:text-muted-foreground focus-visible:outline-none focus-visible:ring-1 focus-visible:ring-ring disabled:cursor-not-allowed disabled:opacity-50",
+                className
+            )}
+            {...props}
+        />
+    );
+}
+
+export { Input };