chore: upgrade to Astro v4

[jbmoelker]

Changes

• upgrade to Astro v4
• upgrade Astro related packages
• fix issues caused by upgrades

Easy peasy with the new npx @astrojs/upgrade:

Associated issue

N/A

How to test

1. Open preview link
2. Verify everything still works as it did before

Checklist

• [x] I have performed a self-review of my own code
• [x] I have made sure that my PR is easy to review (not too big, includes comments)
• I have added/updated tests to prove that my feature works (if not possible please explain why)
• I have made changes to the README and if the change affects the project setup (npm commands changed, new service added, environmental variable added)
• I have added a decision log entry if the change affects the architecture or changes a significant technology
• [x] I have notified a reviewer

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