feature: Minimal page layout

[jbmoelker]

Changes

Minimal page layout styling with flex header and sticky footer.

Associated issue

N/A

How to test

1. Open preview link
2. Review any page
3. Navigate to a page with little content (like /nl/)
4. Verify that the footer sticks to the bottom even though the main content doesn't push it there

Checklist

• I have performed a self-review of my own code
• I have made sure that my PR is easy to review (not too big, includes comments)
• I have made updated relevant documentation files (in project README, docs/, etc)
• I have added a decision log entry if the change affects the architecture or changes a significant technology
• I have notified a reviewer