Polish GitHub Pages hero: full-span banner, tagline, and section spacing.

[timsherwood]

• Make the hero banner span the full viewport width
• Add "register-transfer-level hardware design and simulation" tagline below logo
• Increase spacing above section headings
• Constrain hero button width for readability

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.8%. Comparing base (5a9d67e) to head (2e1c0be).

Additional details and impacted files

@@             Coverage Diff             @@
##           development    #507   +/-   ##
===========================================
  Coverage         93.8%   93.8%           
===========================================
  Files               30      30           
  Lines             7172    7172           
===========================================
  Hits              6722    6722           
  Misses             450     450           

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