fix: header and footer feedback

[stephiescastle]

Checklist

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Description

Addresses https://github.com/nasa-jpl/www/issues/189#issuecomment-2271719519

• Fixes alignment in NavHeading
• Fixes definition of lighter color tokens
• Adds NASA OSTEM link to EDU header/footer components
• Links "Education" in NavDesktopEdu to education homepage

Instructions to test

1. make vue-storybook
2. view: http://localhost:6006/?path=/story/navigation-headers-edu-navdesktopedu--base-story&globals=theme:ThemeEdu

Tested in the following environments/browsers:

Operating System

• macOS
• iOS
• iPadOS
• Windows

Browser

• Chrome
• Firefox ESR
• Firefox
• Safari
• Edge