Fix lesson loading on private GitHub Pages

[Copilot]

Lessons returned HTTP 404 because the site root was inferred from GitHub Pages hostname conventions. Private Pages hosts the workshop at the domain root, causing Markdown requests to include an extra /workshop segment.

Changes

• Resolve the site root relative to the lesson page:

  new URL('../', lessonPageUrl)

• Use the shared resolver for lesson Markdown and target-app URLs.
• Cover private root-hosted and project-path Pages layouts.

[Copilot]

Copilot review overview

🟢 Approval recommended

The relative URL logic is correct for both layouts, and the navigation tests pass.

This review doesn't count toward merge requirements.

Review effort: Balanced
Findings: None

What changed in this PR

Fixes lesson and target-app URL resolution across private and project-path GitHub Pages deployments.

Changes:

• Adds a shared relative site-root resolver.
• Uses it for lesson Markdown and target-app URLs.
• Tests root-hosted and project-path layouts.

File	Description
docs/​workshop/​step.html	Uses the shared site-root resolver.
docs/​language-navigation.js	Adds and exports siteRootUrl.
docs/​tests/​markdown-language-preprocessor.test.js	Covers both Pages layouts.

---

💡 Add a code-review agent skill or configure MCP servers for context-aware, tailored reviews. Learn more in the docs.