Fix stylelint no-descending-specificity error in Footer.css

Reordered CSS selectors to ensure proper specificity ordering:
- Moved all base link selectors (a) before pseudo-class selectors (:hover, :active, :focus)
- Grouped .footer-copyrights and .footer-mission link selectors properly
- This fixes the stylelint error where .footer-copyrights a appeared after .footer-mission a:hover/active/focus

The rule requires less specific selectors to appear before more specific ones to avoid unexpected CSS cascade behavior.

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Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: OpenStaxClaude