Fix navigation issues on dev portal

[Anca2022]

PR Checklist

• Linked issue added (e.g., Fixes #123)
• If blog post was added:
  • Ensure images have been optimised
  • Update dates to reflect the actual publishing date when merged (file names, folder names, and frontmatter)

Summary

Linear issue - DEVPORT-12

This PR updates the nav menu to replace non-navigational <a> tags with <button> elements.
These menu items were previously implemented as links with e.preventDefault() in JavaScript to prevent navigation. This worked locally but failed in production (likely due to Astro’s optimization and bundling process affecting script execution timing)

[JoblersTune]

Ideally we'd still have the site analytics captured for this click. But I think the root of this issue is from the data-umami-event attribute. We had the same problem with the foundation website. Which is why the foundation website uses data-link-label instead. So we should either copy the same approach here, or include the data-umami-event in the button click.

[JoblersTune]

If you inspect element from the live dev portal and view one of the top level menu items and just remove the data-umami-event attribute, you'll see we get the expected behaviour. That is definitely where the issue is.
While I agree buttons are better, I also like to aim to keep the two sites as identical as possible.