feat(mermaid): Markdown 预览安全渲染 Mermaid 图表（strict 清洗 + 懒加载 chunk + 点击放大） (#164)

* feat(mermaid): 新增 mermaid 懒加载 chunk（构建链四处同步 + mermaid 依赖）

tsdown CHUNKS / bundle-route CHUNK_NAMES / chunk-loader ChunkName /
package.json files 同步注册 mermaid chunk；mermaid ^11.16.1 进依赖与
lockfile；chunk 构建注入 uuid 浏览器入口别名，绕开 node:crypto 纯度门。

* feat(mermaid): Markdown 预览安全渲染 mermaid 图表 + 点击放大弹窗

- splitMermaidBlocks 纯函数按 fence 切块，无 mermaid 文件零行为变化；
- mermaid.initialize 走 securityLevel strict + htmlLabels:false，不应用
  bindFunctions（静态图）；渲染 SVG 经 mermaid-sanitize 二次清洗：
  删 foreignObject/script/外来 HTML 元素、剥 @*/on* 属性、移除全部
  href/xlink:href，仅接受 SVG 根，解析失败返回空串；
- 点击图表弹出放大弹窗（滚轮缩放/拖拽平移/快捷键，借鉴 PR #75 交互，
  基于已清洗 SVG 克隆重写，不新增攻击面）；
- 深浅色跟随重渲、失败回退错误条 + 原码、CodeBlock 同款 chrome。

* test(mermaid): splitter/sanitize 单测 + chunk 清单同步 + 挂载冒烟 diagram.md

- mermaid-blocks.spec 10 例 fence 切块语义；
- mermaid-sanitize.spec 8 例 XSS（foreignObject/on*/@*/href/xlink:href/
  script/外来元素/畸形 XML/非 SVG 根）；
- bundle-route / chunk-artifact / manifest-consistency 清单加入 mermaid
  （chunk-artifact 补 addEventListener stub）；
- 挂载冒烟新增 diagram.md：client-mermaid.js 往返、SVG 节点文字、
  点击弹窗 Esc 关闭、preview 模式编辑器隐藏。

* docs(mermaid): 安全渲染设计文档 + lazy-chunks 表 + README 双语更新

设计文档记录基线决策（PR #99 架构 + PR #75 点击放大）、安全模型
（strict/htmlLabels/清洗/href 剥离/无 bindFunctions）、验证与取舍。

* fix(mermaid): sanitizer 属性名大小写归一，堵住混合大小写属性绕过（CR P1）

XML 属性名保留大小写，而输出会经 HTML 解析归一化（dangerouslySetInnerHTML），
oNload/HREF/xlink:HREF 这类混合大小写属性此前会漏过清洗。比较前先
toLowerCase()，按原名删除；新增混合大小写事件/链接属性回归用例。

* fix(mermaid): sanitizer 元素黑名单大小写归一，堵住混合大小写元素绕过（CR P1）

XML 元素名保留大小写，querySelectorAll('script') 等选择器匹配不到
<sCrIpT>/<foreignobject>，而输出经 HTML 解析会被归一化为 SVG
script/foreignObject（可执行/可注入 HTML）。改为遍历全部元素按
localName.toLowerCase() 命中小写黑名单后整节点删除；新增混合大小写
script/foreignObject/外来 HTML 元素回归用例（jsdom 实证：旧选择器
命中 0，新逻辑命中 2）。

* fix(mermaid): 单次 Markdown 解析 + 占位交换（CR P1）+ CommonMark fence 规则（CR P2）

P1（跨 fence 语义）：弃用逐块 MarkdownText 拆分，改为整篇文档单次
MarkdownText 渲染，布局后把 language-mermaid 代码块交换为 MermaidDiagram
（React 管理的 .md-code-block 宿主保留在树中、display:contents 抑制盒子，
协调安全；块不再 mermaid 时还原原 children）。新增
tests/mermaid-markdown.spec.tsx 与 e2e 跨 fence 引用链接断言。

P2（fence 匹配）：支持 3+ 反引号与波浪号开 fence；闭 fence 须同字符且
长度不小于开 fence；反引号 info string 含反引号不视为开 fence；修复
带缩进开 fence 的 info 提取。blocks 单测 +3 例。

src/client/TextEditor.tsx

@@ -13,7 +13,8 @@
  * the FileViewerProps toolbar callbacks so the host's path-input header
  * renders the controls instead.
  */
-import { useEffect, useRef, useState } from 'react'
+import { useEffect, useMemo, useRef, useState } from 'react'
+import type { ComponentType } from 'react'
 import { createPortal } from 'react-dom'
 import clsx from 'clsx'
 import { EditorState } from '@codemirror/state'
@@ -27,6 +28,8 @@ import { isDarkScheme, subscribeColorScheme } from './theme.ts'
 import { SandboxStatusBar } from './SandboxStatusBar.tsx'
 import { appendToDraft } from './conversation-draft.ts'
 import { buildSelectionInsert, linesOfSelection } from './selection-payload.ts'
+import { lazyChunkComponent } from './lazy-chunk.tsx'
+import { splitMermaidBlocks, type MermaidMarkdownProps } from './mermaid-blocks.ts'
 import { t } from './locales.ts'
 import type { EditorToolbarState, FileViewerProps } from './service.ts'
 import css from './sidebar.module.css'
@@ -41,6 +44,16 @@ interface SelectionPopup {
   top: number
 }
 
+/**
+ * The chunk-resident markdown preview renderer (mermaid lazy chunk): one
+ * MarkdownText pass over the whole source, with rendered mermaid fences
+ * swapped for diagrams. Module-level `pick` keeps the load effect stable.
+ */
+const LazyMermaidMarkdown = lazyChunkComponent<MermaidMarkdownProps>(
+  'mermaid',
+  (mod) => mod.MermaidMarkdown as ComponentType<MermaidMarkdownProps> | undefined,
+)
+
 /**
  * The sandbox tokens of the HTML preview iframe. NO allow-same-origin (the
  * preview must stay in an opaque origin — with the route's own origin it
@@ -237,6 +250,19 @@ export function TextEditor(props: FileViewerProps) {
 
   const markdown = viewerId === 'markdown'
   const html = viewerId === 'html'
+  /** The markdown source the preview renders (draft wins over saved content). */
+  const mdText = draft ?? content ?? ''
+  /** md/mermaid block split for the preview (mermaid fences lift out). Split
+   *  only in preview mode: edit-mode keystrokes must not re-scan the source. */
+  const mdBlocks = useMemo(
+    () => (markdown && mode === 'preview' ? splitMermaidBlocks(mdText) : []),
+    [markdown, mode, mdText],
+  )
+  const hasMermaid = useMemo(
+    () => mdBlocks.some(block => block.kind === 'mermaid'),
+    [mdBlocks],
+  )
+  const codeLabels = { copyLabel: t('copy'), copiedLabel: t('copied') }
 
   /**
    * Selection popup for the markdown preview: a mouse-up inside the preview
@@ -263,7 +289,7 @@ export function TextEditor(props: FileViewerProps) {
       return
     }
     const rect = sel.getRangeAt(0).getBoundingClientRect()
-    const lines = linesOfSelection(draft ?? content ?? '', text)
+    const lines = linesOfSelection(mdText, text)
     showPopup(
       buildSelectionInsert(path, scope.cwd, lines ?? undefined, text),
       rect.left + rect.width / 2,
@@ -361,11 +387,13 @@ export function TextEditor(props: FileViewerProps) {
               dictionary: the DSH MarkdownText/CodeBlock are cordis-free and
               fall back to hardcoded Chinese otherwise (same pattern as the
               chat's AssistantMarkdown). Render-time t() keeps them following
-              the active locale on live switches. */}
-          <MarkdownText
-            text={draft ?? content ?? ''}
-            codeLabels={{ copyLabel: t('copy'), copiedLabel: t('copied') }}
-          />
+              the active locale on live switches. Mermaid fences hand the
+              whole document to the mermaid lazy chunk (single markdown
+              parse; cross-fence references/footnotes stay intact); files
+              without one render exactly as before. */}
+          {hasMermaid
+            ? <LazyMermaidMarkdown text={mdText} codeLabels={codeLabels} />
+            : <MarkdownText text={mdText} codeLabels={codeLabels} />}
         </div>
       )}
       {html && mode === 'preview' && (