Add localized Copilot app workshop docs

[justinyoo]

Summary

Add localized GitHub Copilot app workshop content for Spanish (Spain), Japanese, Korean, Portuguese (Brazil), and Simplified Chinese. Configure Starlight's built-in locale routing and language selector, and add the localization rules and repository guidance needed to maintain the translated content.

Type of change

• Workshop content (lesson Markdown, images)
• Site shell (docs/ Astro + Starlight wrapper)
• Copilot configuration (.github/copilot-instructions.md, instructions, agents, skills)
• Repo housekeeping (CI, dependabot, README, license)
• Other:

Verification

• cd docs && rm -rf dist && npm run build succeeds (target: 36 routes × 6 locales + 1 redirect = 217 built pages excluding 404; build reports 218 HTML files including 404, or note any intentional change)
• Lychee link check passes:
  mkdir -p /tmp/lychee-root && ln -sfn $PWD/docs/dist /tmp/lychee-root/agents-in-sdlc && lychee --offline --no-progress --root-dir /tmp/lychee-root 'docs/dist/**/*.html'
• External GitHub URLs that I changed have been clicked manually (lychee runs offline)

Screenshots

Not included. The language selector uses Starlight's built-in header and mobile-menu components.

Notes for reviewers

The branch contains three commits:

• c381a99 adds the five localized content sets and locale-specific translation rules.
• 0f59fb2 configures the Starlight locales and selector, places translated pages at locale-root routes, and updates localization and page-count guidance.
• 700e6c9 fixes four Korean and Chinese localhost links identified by the offline link check.

npm run check completed with 0 errors, warnings, or hints. The clean production build generated the expected 218 HTML pages including the 404 page. Lychee checked 19,072 references and completed with 0 errors.