docs: add DEPLOYMENT.md for historical versions (#23151)

[zhouzhiouhub]

Related Issue

Reference #23151

Changes

• Added DEPLOYMENT.md to document the deployment process for historical versions.
• Includes a branch-to-domain mapping table, deployment trigger mechanisms, and a manual deployment fallback plan.
• Added guidelines for maintaining historical versions.

Notes

This PR provides supporting documentation for #23151. Once DNS configuration is complete, maintainers can refer to this document to carry out subsequent deployments.

cc @bluwy @sapphi-red

[vercel]

@zhouzhiouhub is attempting to deploy a commit to the vuejs Team on Vercel.

A member of the Team first needs to authorize it.

[dogledogle]

感谢你关注并提交这个 PR！

目前 sapphi-red 正在推进相关部署工作，计划将部署迁移到 Cloudflare，以便后续能够直接管理部署环境。由于这次迁移还涉及一些基础设施方面的调整，因此可能还需要一些时间。

考虑到部署工作尚未完成，最终采用的平台、访问域名、部署方式以及后续维护流程等细节目前仍存在一定的不确定性。如果现在就添加配套文档，后续方案发生变化时，文档可能需要再次修改，也可能在这段过渡期内给读者带来困惑。

因此，我建议先耐心等待部署和相关方案确定，待功能可以稳定访问、维护流程也明确之后，再根据最终实现补充文档。这样能够确保文档内容准确、可验证，也能减少不必要的重复调整。