[codex] shorten generated page titles

[Sean-Kenneth-Doherty]

Summary

• shorten the homepage <title> so it stays under common SEO title-length guidance
• shorten the open-source guide page title and matching title metadata/headline
• keep the article wording beginner-focused while avoiding generated long-title validation errors

Addresses #348

Validation

• git diff --check
• GITHUB_TOKEN=$(gh auth token) pnpm build
• generated title check: homepage title is 62 chars; guide title is 50 chars
• pnpm dlx html-validate dist/index.html dist/contribute-to-opensource/index.html no longer reports long-title errors; remaining reports are existing nested-anchor/article-lang issues covered by other PRs

[Sean-Kenneth-Doherty]

Validation notes for this title-length slice:

• git diff --check passes
• GITHUB_TOKEN=$(gh auth token) pnpm build passes
• generated homepage title is now 62 characters: First Contributions - Make Your First Open Source Contribution
• generated guide title is now 50 characters: How to Contribute to Open Source: A Beginner Guide
• pnpm dlx html-validate dist/index.html dist/contribute-to-opensource/index.html no longer reports long-title; the remaining validator findings are the pre-existing nested-anchor/article-lang items already covered by other open PRs