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/toaster.tsx

@@ -0,0 +1,35 @@
+"use client"
+
+import { useToast } from "@/components/hooks/use-toast"
+import {
+  Toast,
+  ToastClose,
+  ToastDescription,
+  ToastProvider,
+  ToastTitle,
+  ToastViewport,
+} from "@/components/ui/toast"
+
+export function Toaster() {
+  const { toasts } = useToast()
+
+  return (
+    <ToastProvider>
+      {toasts.map(function ({ id, title, description, action, ...props }) {
+        return (
+          <Toast key={id} {...props}>
+            <div className="grid gap-1">
+              {title && <ToastTitle>{title}</ToastTitle>}
+              {description && (
+                <ToastDescription>{description}</ToastDescription>
+              )}
+            </div>
+            {action}
+            <ToastClose />
+          </Toast>
+        )
+      })}
+      <ToastViewport />
+    </ToastProvider>
+  )
+}