Update Next.js to v15

[joshka]

bump caniuse db

https://github.com/browserslist/browserslist#browsers-data-updating

fix sed command to work with both GNU and MacOS sed

The sed command which replaces the markdown import in the api.js file was not working on MacOS because the -i flag requires an argument with the backup file extension. This commit adds the .bak extension to the sed command to make it work on both GNU and MacOS sed (and then removes the backup file).

Update to next.js 14

• "next build export" is replaced with an output config option https://nextjs.org/docs/app/building-your-application/deploying/static-exports
• "next start" is not compatible with static exports and has been removed from the package scripts
• blog rss feed is now generated to out/blog/index.xml instead of _next/static/feed.xml to work with the default output and the redirect in netlify.toml has been reversed so that rss feed requests are redirected to the new location

Upgrade to nextjs 15

• Use turbopack instead of webpack
• User typescript instead of js for next config
• silence deprecation warnings on bulma sass problems. Bulma 1.0.2 breaks a bunch of things that worked in 0.8 so it's difficult to update to without changing how the site looks.