[WIP] Rewrite website to generate links to helix-toolkit pages

[Copilot]

• Understand the requirement from @holance
• Update links in _config.yml to use github.io URLs and add pages config
• Update sidebar.html to replace docs.helix-toolkit.org with github.io link
• Update sidebar.html to add Projects section with links to helix-toolkit and helix-toolkit-nex
• Update index.md to replace helix-toolkit.org links with github.io links
• Add link to helix-toolkit-nex repository in index.md
• Validate YAML syntax is correct
• Verify changes render correctly when site is deployed

Original prompt

Rewrite the website to generate links to other github.io pages/repositories under helix-toolkit org

---

💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.

[holance]

@copilot Rewrite website to generate links to helix-toolkit io pages for helix-toolkit and helix-toolkit-nex repos

[Copilot]

@copilot Rewrite website to generate links to helix-toolkit io pages for helix-toolkit and helix-toolkit-nex repos

Updated the website to use GitHub Pages links. Changes made in commit d38e641:

• Replaced all helix-toolkit.org domain references with helix-toolkit.github.io URLs
• Updated _config.yml to use HTTPS and added a pages configuration with links to helix-toolkit, helix-toolkit-nex, and docs repos
• Updated sidebar to include a Projects section with direct links to both Helix Toolkit and Helix Toolkit Nex repositories
• Updated main page to reference the helix-toolkit-nex project and use GitHub Pages URLs throughout

All links now point to the respective GitHub Pages under the helix-toolkit organization.