feat: Add comprehensive shadcn/ui component library

Install 35 shadcn components for standard business application:

Base: Button, Input, Label, Card
Forms: Form, Select, Checkbox, Radio, Switch, Textarea
Auth/Feedback: Dialog, Alert, AlertDialog, Toast, Sonner
Dashboard: Table, Tabs, Avatar, Badge, Dropdown, Popover, Tooltip
Navigation: NavigationMenu, Sidebar, Breadcrumb, Sheet, Command
Data Display: Skeleton, Progress, Separator, ScrollArea, Collapsible,
              Accordion, Pagination

Includes hooks (use-toast, use-mobile) and updated Tailwind config.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/components/ui/sonner.tsx

@@ -0,0 +1,45 @@
+"use client"
+
+import {
+  CircleCheck,
+  Info,
+  LoaderCircle,
+  OctagonX,
+  TriangleAlert,
+} from "lucide-react"
+import { useTheme } from "next-themes"
+import { Toaster as Sonner } from "sonner"
+
+type ToasterProps = React.ComponentProps<typeof Sonner>
+
+const Toaster = ({ ...props }: ToasterProps) => {
+  const { theme = "system" } = useTheme()
+
+  return (
+    <Sonner
+      theme={theme as ToasterProps["theme"]}
+      className="toaster group"
+      icons={{
+        success: <CircleCheck className="h-4 w-4" />,
+        info: <Info className="h-4 w-4" />,
+        warning: <TriangleAlert className="h-4 w-4" />,
+        error: <OctagonX className="h-4 w-4" />,
+        loading: <LoaderCircle className="h-4 w-4 animate-spin" />,
+      }}
+      toastOptions={{
+        classNames: {
+          toast:
+            "group toast group-[.toaster]:bg-background group-[.toaster]:text-foreground group-[.toaster]:border-border group-[.toaster]:shadow-lg",
+          description: "group-[.toast]:text-muted-foreground",
+          actionButton:
+            "group-[.toast]:bg-primary group-[.toast]:text-primary-foreground",
+          cancelButton:
+            "group-[.toast]:bg-muted group-[.toast]:text-muted-foreground",
+        },
+      }}
+      {...props}
+    />
+  )
+}
+
+export { Toaster }