Merge origin/main (#984, the canvas shell) into the cleanup branch

Conflicts resolved in 16 files. Where main's new shell, classic page and
tests depend on a wire format or a signature the cleanup had changed, main
wins; where main only extended code the cleanup had restructured, main's
change is carried over into the new structure:

- MCP HTTP server: the poll response keeps main's separate export fields
  (exportFormat, exportXml, exportOptions, exportId with a random id)
  instead of the cleanup's pendingExport object; the classic preview page
  is main's version
- MCP index: start_session keeps the cleanup's structure and gains main's
  BROWSER=none, previewUrl and same-origin note; get_selection is written
  in the registerTool style; create_new_diagram keeps the cleanup's
  helpers with main's comment
- history: addHistory takes main's source parameter and returns the index
  again (main's signature)
- new-diagram: the cleanup's prepareNewModel split plus main's page ids
  for diagrams without one
- diagram context: one ExportResult type (main's, with optional fields)
  for both the tagged exports and main's requestExport; the cleanup's
  single export resolver stays
- versions store and version-text test: main's VersionItem base type and
  describeChangeSummary rename, without the legacy history conversion the
  cleanup removed
- dictionaries: main's shell section added; openFileHint stays removed
  (unused on main too)
- tests: the server wiring test keeps the SDK client and gains main's
  session cases; the HTTP server test uses main's export fields; the DOM
  polyfill comes from tests/setup.ts
- package.json: main's postcss kept, the cleanup's removals kept; lockfile
  regenerated

docs/cn/README_CN.md

@@ -114,6 +114,8 @@ claude mcp add drawio -- npx @next-ai-drawio/mcp-server@latest
 然后对 AI 说"画一个用户认证流程图，包含登录、MFA 和会话管理"，图会实时出现在浏览器里。MCP 服务器包含网页版的大部分画图能力：
 
 -   同一套画图规则和图标库（AWS、Azure、GCP、Kubernetes 等）
+-   预览页就是网页版的画布：AI 的改动会被标出，按一次 Ctrl+Z 就能撤销，AI 还能读到你选中的图形
+-   draw.io 编辑器随包一起安装，装好后预览不需要联网（也可以用 `DRAWIO_BASE_URL` 改用外部的 draw.io）
 -   截图工具，AI 可以看一眼画好的图并自行修正
 -   版本历史、多页图表，下载为 `.drawio`、`.png`、`.svg` 或 `.drawio.svg`
 -   自动保存到 `~/.next-ai-drawio/`，重启后接着画

docs/cn/offline-deployment.md

@@ -14,7 +14,7 @@ Next AI Draw.io 自带一份 draw.io。`npm run build`（包括 Docker 构建）
 
 构建会从 [draw.io 发布页](https://github.com/jgraph/drawio/releases) 下载 `draw.war`（约 50 MB）。如果构建机器访问不了 GitHub：
 
-- 在另一台机器上下载 `scripts/fetch-drawio.mjs` 里写明的那个版本的 `draw.war`，解压到 `public/drawio`（删掉 `WEB-INF` 和 `META-INF`），再把版本号（例如 `v32.0.2`）写进 `public/drawio/.version`。构建时就会使用这份副本。
+- 在另一台机器上下载 `packages/mcp-server/src/drawio-version.json` 里写明的那个版本的 `draw.war`，解压到 `public/drawio`（删掉 `WEB-INF` 和 `META-INF`），再把版本号（例如 `v32.0.2`）写进 `public/drawio/.version`。构建时就会使用这份副本。
 - 或者在能联网的机器上构建镜像，再拷到离线网络里。
 
 ## 来自其他网站的图片