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

components.json

@@ -0,0 +1,21 @@
+{
+    "$schema": "https://ui.shadcn.com/schema.json",
+    "style": "new-york",
+    "rsc": false,
+    "tsx": false,
+    "tailwind": {
+        "config": "",
+        "css": "src/admin/styles/globals.css",
+        "baseColor": "neutral",
+        "cssVariables": true,
+        "prefix": ""
+    },
+    "aliases": {
+        "components": "@/components",
+        "utils": "@/lib/utils",
+        "ui": "@/components/ui",
+        "lib": "@/lib",
+        "hooks": "@/hooks"
+    },
+    "iconLibrary": "hugeicons"
+}