Add package-lock.json to .gitignore

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This repo uses pnpm (pnpm-lock.yaml, pnpm-workspace.yaml, .npmrc). package-lock.json should not appear in the repository.

• Add package-lock.json to .gitignore

Original prompt

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This section details on the original issue you should resolve

<issue_title>Proposal: rename RenderCanvas to RenderRoot</issue_title>
<issue_description>One item that kept tripping me up was the name RenderCanvas. It's odd because it owns a <canvas> in this._el. What about RenderRoot?

• Clear: it's the root of the render tree
• Follows existing convention (Render prefix)
• Similar to React's FiberRoot, Flutter's RenderView
• No confusion with canvas elements</issue_description>

<agent_instructions>根据 Issue 的要求，实现需求，不要忘记更新单元测试</agent_instructions>

Comments on the Issue (you are @copilot in this section)

• Fixes Proposal: rename RenderCanvas to RenderRoot #33

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