Webpage: automate changelog page generation and navigation integration

[romanstingler]

Add a sync-changelog.mjs script that generates website/src/pages/changelog.md from the repository CHANGELOG.md, rendering each release as a collapsible details card. Wire the script into the gh-pages-deploy workflow so the changelog page stays in sync on every deploy. Update docusaurus.config.ts to index pages for search, and add Changelog links to the left navbar and the "More" dropdown menu. Include styling for the changelog release cards in custom.css.

@MalpenZibo I hope you don't mind me messing with the webpage. 😄

[MalpenZibo]

Make sense but two things:

• with this we have a duplicate change log file (the one in the root and the MD generated). We could hit ignore the one generated but then a local pnpm start doesn't generate that file
• the MDX conversion could lead to other possible problems. That regex replace is enough for every possible cases?