feat(ui): 重构核心 UI 组件库，新增 shadcn/ui 组件

- 重构 Button、Card、Badge、Input、Textarea 等基础组件
- 新增 Accordion、Alert、Dialog、Dropdown、Form 等 shadcn/ui 组件
- 新增 AnimatedCounter、StatsShowcase、MetricCard 等数据展示组件
- 新增 ScrollReveal 滚动动画组件
- 重构 Toast 通知系统与 Tooltip 提示组件
- 更新设计令牌系统，对齐新品牌视觉

src/components/ui/checkbox.tsx

@@ -0,0 +1,44 @@
+'use client';
+
+import * as React from 'react';
+import * as CheckboxPrimitive from '@radix-ui/react-checkbox';
+import { Check, Minus } from 'lucide-react';
+import { cn } from '@/lib/utils';
+
+/**
+ * 标准 shadcn/ui Checkbox 组件
+ * 基于 @radix-ui/react-checkbox
+ */
+const Checkbox = React.forwardRef<
+  React.ElementRef<typeof CheckboxPrimitive.Root>,
+  React.ComponentPropsWithoutRef<typeof CheckboxPrimitive.Root>
+>(({ className, ...props }, ref) => (
+  <CheckboxPrimitive.Root
+    ref={ref}
+    data-slot="checkbox"
+    className={cn(
+      'peer size-4 shrink-0 rounded-sm border border-border-primary bg-bg-primary shadow-sm',
+      'focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-brand focus-visible:ring-offset-2',
+      'disabled:cursor-not-allowed disabled:opacity-50',
+      'data-[state=checked]:bg-brand data-[state=checked]:text-white data-[state=checked]:border-brand',
+      'data-[state=indeterminate]:bg-brand data-[state=indeterminate]:text-white data-[state=indeterminate]:border-brand',
+      'transition-colors duration-fast',
+      className
+    )}
+    {...props}
+  >
+    <CheckboxPrimitive.Indicator
+      data-slot="checkbox-indicator"
+      className={cn('flex items-center justify-center text-current')}
+    >
+      {props.checked === 'indeterminate' ? (
+        <Minus className="size-3.5" />
+      ) : (
+        <Check className="size-3.5" />
+      )}
+    </CheckboxPrimitive.Indicator>
+  </CheckboxPrimitive.Root>
+));
+Checkbox.displayName = CheckboxPrimitive.Root.displayName;
+
+export { Checkbox };