Add meta-pipelines hackathon project for Barcelona 2026 - #4447

Changed pages include:

• index.html - view
• 404.html - view
• about.html - view
• advisories.html - view
• blog.html - view
• code_of_conduct.html - view
• contributors.html - view
• events.html - view
• governance.html - view
• join.html - view

There are more changes not included in the list