style(组件): 调整新对话弹窗圆角样式

将弹窗圆角从 rounded-xl 改为 rounded-md，与其他弹窗保持一致

src/components/features/NewChatModal.tsx

@@ -185,7 +185,7 @@ export function NewChatModal({ isOpen, onClose }: NewChatModalProps) {
     >
       <div
         ref={modalRef}
-        className="w-full max-w-2xl bg-[var(--color-bg-primary)] rounded-xl shadow-2xl overflow-hidden animate-scale-in"
+        className="w-full max-w-2xl bg-[var(--color-bg-primary)] rounded-md shadow-2xl overflow-hidden animate-scale-in"
       >
         {/* 标题栏 */}
         <div className="flex items-center justify-between px-6 py-4 border-b border-[var(--color-border)]">