feat(chat): support render empty prompt

[mortalYoung]

变更类型

请选择以下选项以描述 PR 的类型：

• Bug 修复（修复现有问题）
• 新功能（添加了一个功能）
• 代码优化（性能改进、代码重构）
• 文档更新
• 单测新增或修改
• 其他（请说明）：

相关问题

变更内容

• 优化提问为空的 Prompt 渲染
• 优化 react-markdown 的渲染，避免 validateDOMNesting 问题

详细描述

对应 Previewer

[Copilot]

Pull Request Overview

This PR introduces a new feature to support rendering an empty prompt and optimizes the rendering behavior for both typing effects and markdown content, particularly to avoid HTML splitting and validateDOMNesting issues.

• Introduces a helper function in the typing effect to ensure HTML tags aren’t split.
• Adds a guard to the prompt component to return null when no title is provided.
• Modifies the markdown rendering to conditionally use a div element to prevent DOM nesting errors.

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
src/useTyping/index.ts	Adds a helper function to calculate the next chunk position without splitting HTML tags.
src/chat/prompt/index.tsx	Returns null for empty prompts based on a missing title field.
src/chat/markdown/index.tsx	Adjusts paragraph rendering to avoid validateDOMNesting errors with non-text children.

Comments suppressed due to low confidence (2)

src/chat/prompt/index.tsx:31

• [nitpick] Consider adding a comment here to clarify why the component returns null when 'data.title' is missing, helping maintain readability and understandability of the logic.

if (!data?.title) return null;

src/chat/markdown/index.tsx:51

• [nitpick] While the conditional rendering prevents validateDOMNesting errors, verify that using a
  instead of a

  for mixed content does not affect the intended semantics or accessibility of the output.

p: (data) => {