Add Lesson detail pages feature

[gaurirathi]

This PR adds individual lesson detail pages at the /lessons/[slug] route.

Each lesson now has its own page that displays full metadata and provides a clear link to the external lesson resource, instead of navigating directly away from the site.

##What’s included

• Dynamic lesson route at src/pages/lessons/[slug].astro
• Slug generation from lesson names
• Lesson detail page layout following existing UC branding
• Display of lesson metadata (name, description, educational level, OSS role, etc.)
• “View External Lesson” button that opens in a new tab
• Breadcrumb navigation back to the lessons library
• Responsive layout for mobile and desktop

This improves navigation and allows learners to view lesson context before leaving the site.

Closes #28

[github-actions]

❌ PR checks failed

One or more validation checks failed. Please review the workflow logs to see what went wrong.

Common issues:

• 📊 Data validation: Google Sheets CSV is unreachable or has invalid data
• 🔍 TypeScript check: Type errors in code
• 🏗️ Build: Build process failed
• 📄 Critical pages: Missing required pages (index, lessons, pathways)
• 🔗 Internal links: Broken links detected

[github-actions]

❌ PR checks failed

One or more validation checks failed. Please review the workflow logs to see what went wrong.

Common issues:

• 📊 Data validation: Google Sheets CSV is unreachable or has invalid data
• 🔍 TypeScript check: Type errors in code
• 🏗️ Build: Build process failed
• 📄 Critical pages: Missing required pages (index, lessons, pathways)
• 🔗 Internal links: Broken links detected

[github-actions]

❌ PR checks failed

One or more validation checks failed. Please review the workflow logs to see what went wrong.

Common issues:

• 📊 Data validation: Google Sheets CSV is unreachable or has invalid data
• 🔍 TypeScript check: Type errors in code
• 🏗️ Build: Build process failed
• 📄 Critical pages: Missing required pages (index, lessons, pathways)
• 🔗 Internal links: Broken links detected

[github-actions]

✅ All PR checks passed!

Check	Status
📊 Data validation	✅ Pass
🔍 TypeScript check	✅ Pass
🏗️ Build	✅ Pass
📄 Critical pages	✅ Pass
🔗 Internal links	✅ Pass

The site builds successfully and all validation checks passed.

[ShouzhiWang]

Thank you for putting this together. The functionality of having dedicated lesson pages is definitely valuable.

However, we noticed some significant visual issues during testing (e.g., text visibility in the sidebar is extremely low/illegible in some modes, and the layout hierarchy is inconsistent).

Recommendation: We have actually just received a comprehensive new design draft for the entire website from our designer. To avoid you spending time polishing a design that is about to be completely replaced, I would like to suggest pause work on this PR.

[jt14den]

Hi @gaurirathi, thank you for this work. We have an internal team member (@ShouzhiWang) currently implementing the lesson detail architecture to match our specific backend requirements. To avoid duplication, we are going to close this PR in favor of #63. We'd love your help on issues labeled help wanted instead! We are still staging things for next milestone.