feat: add Open Graph and Twitter Card metadata for social sharing

[Aniket-The-TechWhiz]

Summary

This PR adds Open Graph and Twitter Card metadata to src/index.html to improve link previews when the site is shared on platforms such as LinkedIn, X (Twitter), Slack, Discord, and WhatsApp.

Changes Made

• Added og:title
• Added og:description
• Added og:type with the value website
• Added og:url pointing to the live GitHub Pages site
• Added twitter:card with the value summary
• Grouped all social metadata under a descriptive comment for easier maintenance

Notes

• Reused the existing page title and meta description to keep metadata consistent.
• Used the production URL: https://ayushmore1214.github.io/FirstCommit/.
• og:image was intentionally not added because a hosted image is not currently available. The issue notes that adding the text metadata alone is a complete and valuable improvement.

[Ayushmore1214]

Thanks @Aniket-The-TechWhiz. The Open Graph and Twitter Card tags themselves are correct, and skipping og:image for now is a reasonable call. Three things to sort out:

1. Missing DCO sign-off. Neither commit on this branch has a Signed-off-by: line, so the DCO check will fail. Sign off both commits:

git rebase --signoff upstream/main
git push --force-with-lease

2. This branch includes the Draft PR glossary card from #59. It looks like you branched off add-draft-pr-glossary instead of main. Once #59 is merged that overlap will disappear on its own, so easiest path: fix #59 first, then rebase this branch onto the updated main so this PR contains only the meta tags.

3. Unrelated reformatting. The existing description meta tag and the Google Fonts <link> got rewrapped onto multiple lines. Please revert those two back to their original single-line form so the diff shows only what this PR is actually adding. Keeping diffs focused makes review much faster, and it's a habit worth building.

After that this is good to go. It closes #49.