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/badge.tsx

@@ -0,0 +1,36 @@
+import * as React from "react"
+import { cva, type VariantProps } from "class-variance-authority"
+
+import { cn } from "@/lib/utils"
+
+const badgeVariants = cva(
+  "inline-flex items-center rounded-full border px-2.5 py-0.5 text-xs font-semibold transition-colors focus:outline-none focus:ring-2 focus:ring-ring focus:ring-offset-2",
+  {
+    variants: {
+      variant: {
+        default:
+          "border-transparent bg-primary text-primary-foreground hover:bg-primary/80",
+        secondary:
+          "border-transparent bg-secondary text-secondary-foreground hover:bg-secondary/80",
+        destructive:
+          "border-transparent bg-destructive text-destructive-foreground hover:bg-destructive/80",
+        outline: "text-foreground",
+      },
+    },
+    defaultVariants: {
+      variant: "default",
+    },
+  }
+)
+
+export interface BadgeProps
+  extends React.HTMLAttributes<HTMLDivElement>,
+    VariantProps<typeof badgeVariants> {}
+
+function Badge({ className, variant, ...props }: BadgeProps) {
+  return (
+    <div className={cn(badgeVariants({ variant }), className)} {...props} />
+  )
+}
+
+export { Badge, badgeVariants }