feat(client): UI primitives 基线（E2）

- 引入 Radix Dialog/DropdownMenu/Tabs + CVA
- 新增 Button/Input/Dialog/Tabs/Table/Card 等组件（本地拷贝单向同步）
- 增加 touch-target(44px) 样式基础

client/src/components/ui/button.tsx

@@ -0,0 +1,51 @@
+import * as React from "react";
+import { Slot } from "@radix-ui/react-slot";
+import { cva, type VariantProps } from "class-variance-authority";
+import { cn } from "../../lib/utils";
+
+const buttonVariants = cva(
+  "inline-flex items-center justify-center whitespace-nowrap rounded-lg text-sm font-medium transition-colors focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-primary-200 disabled:pointer-events-none disabled:opacity-50",
+  {
+    variants: {
+      variant: {
+        default: "bg-primary text-white hover:bg-primary-600",
+        secondary: "border border-slate-200 bg-white text-slate-700 hover:bg-slate-50",
+        outline: "border border-slate-200 bg-transparent text-slate-900 hover:bg-slate-50",
+        destructive: "bg-red-600 text-white hover:bg-red-700",
+        ghost: "bg-transparent text-slate-700 hover:bg-slate-100",
+        link: "bg-transparent text-primary underline-offset-4 hover:underline",
+      },
+      size: {
+        default: "h-11 px-4",
+        sm: "h-10 rounded-md px-3 text-xs",
+        lg: "h-12 rounded-xl px-6 text-base",
+        icon: "h-11 w-11 p-0",
+      },
+    },
+    defaultVariants: {
+      variant: "default",
+      size: "default",
+    },
+  },
+);
+
+export type ButtonProps = React.ButtonHTMLAttributes<HTMLButtonElement> &
+  VariantProps<typeof buttonVariants> & {
+    asChild?: boolean;
+  };
+
+export const Button = React.forwardRef<HTMLButtonElement, ButtonProps>(
+  ({ className, variant, size, asChild = false, ...props }, ref) => {
+    const Comp = asChild ? Slot : "button";
+    return (
+      <Comp
+        className={cn(buttonVariants({ variant, size, className }))}
+        ref={ref}
+        {...props}
+      />
+    );
+  },
+);
+
+Button.displayName = "Button";
+