docs(site): render Markdown task lists

[ShigureNyako]

What

• Render Markdown task-list markers as disabled checkboxes in the VitePress documentation.
• Remove duplicate list bullets and align the generated checkbox controls with their task text.
• Keep the change limited to the documentation renderer, its task-list styling, and the renderer dependency.

Why

The English and Chinese contribution checklists already store each task on its own valid - [ ] ... source line. However, VitePress's Markdown pipeline does not enable GitHub-style task lists by default, so the built pages emitted literal [ ] text instead of checkbox controls.

How

Configure VitePress to use the established markdown-it-task-lists plugin recommended by the VitePress maintainers in vuejs/vitepress#1923. The plugin recognizes [ ], [x], and [X] list-item markers, emits disabled checkbox inputs, and tags the generated list markup for scoped theme styling.

Testing

• pre-commit run --all-files passes
• Tests pass (pytest tests/) — GitHub CI passed on Python 3.10, 3.11, and 3.12
• New tests added (not applicable; generated HTML was inspected directly)
• Documentation updated (if applicable)

Additional validation:

• npm run docs:build — passed; generated all four OpenAPI specs and completed the VitePress build.
• Generated-HTML check — confirmed 72 source task items become 72 disabled checkbox inputs, including five each in the English and Chinese contribution pages.
• Repository-wide Markdown scan — confirmed every checkbox marker is a single standalone task-list item and no source line contains multiple task markers.
• GitHub CI — Pre-commit Checks, Lint, and tests on Python 3.10/3.11/3.12 all passed.

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update
• Refactoring (no functional changes)
• Performance improvement
• CI/CD or build changes

Screenshots / Logs

Local VitePress builds of the same Chinese contribution-guide section at origin/main and this PR's head:

Before	After

[SigureMo]

话说你能在 PR 描述里加一下 before / after 的局部截图吗？

[ShigureNyako]

已补充完成：PR 描述的 Screenshots / Logs 现在并排展示 before / after 局部截图。两张图分别来自同一中文贡献指南页面在 origin/main 和当前 PR head 8effd20 的本地 VitePress build。

[SigureMo]

LGTMeow