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/textarea.tsx

@@ -0,0 +1,22 @@
+import * as React from "react";
+import { cn } from "../../lib/utils";
+
+export type TextareaProps = React.TextareaHTMLAttributes<HTMLTextAreaElement>;
+
+export const Textarea = React.forwardRef<HTMLTextAreaElement, TextareaProps>(
+  ({ className, ...props }, ref) => {
+    return (
+      <textarea
+        className={cn(
+          "flex min-h-[120px] w-full rounded-lg border border-slate-300 bg-white px-3 py-2 text-sm text-slate-900 placeholder:text-slate-400 focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-primary-200 disabled:cursor-not-allowed disabled:opacity-50",
+          className,
+        )}
+        ref={ref}
+        {...props}
+      />
+    );
+  },
+);
+
+Textarea.displayName = "Textarea";
+