docs: fix internal links to preserve localized docs flow

[zyl1121]

Motivation

The Chinese templates troubleshooting page had a broken language flow: clicking the Bring Your Own Image link opened the English docs page instead of staying in the Chinese docs tree.

While checking that issue, I found a few similar internal documentation links that were hard-coded to published .html URLs or older English docs paths.

What Changed

This PR replaces internal CubeSandbox documentation links with relative .md links where appropriate.

Specifically, it fixes:

• the Chinese templates troubleshooting BYOI link
• the matching English templates troubleshooting BYOI link
• internal blog cross-links in the EN/ZH agent-friendly service posts
• network-hardening links in the one-click deployment READMEs
• old GitHub links in the Chinese template build practice guide that pointed at older English docs

Changed files:

• docs/zh/guide/troubleshooting/templates.md
• docs/guide/troubleshooting/templates.md
• docs/zh/guide/tutorials/template-build-practice.md
• docs/zh/blog/posts/2026-06-17-cubesandbox-agent-friendly-service.md
• docs/blog/posts/2026-06-17-cubesandbox-agent-friendly-service.md
• deploy/one-click/README.md
• deploy/one-click/README_zh.md

Why Relative Links

Relative .md links are better for internal documentation references because they:

• keep readers in the correct language tree
• work in local VitePress preview
• avoid hard-coding the production domain
• work better for forks and mirrors
• let VitePress resolve the final .html output path

Validation

• searched Markdown/MDX files for remaining cubesandbox.com/...html links
• searched docs and README files for remaining internal .html links, excluding third-party references
• ran git diff --check

Scope

This PR only updates documentation links. It does not change runtime behavior, APIs, CLI behavior, or documentation content semantics.