Reduce marketing interaction main-thread work

[zahlekhan]

Summary

• replace Motion-based marketing accordion and mobile-menu animation with CSS transitions/animations
• replace the animated brand-logo hover state with CSS
• stop fetching and animating the live GitHub star count in critical header chrome
• remove the requestAnimationFrame star count-up loop
• make the marketing navbar and footer server-renderable
• replace generated footer SVG IDs with stable scoped IDs
• remove redundant mounted-state effects from theme-sensitive controls
• add an accessible label to the Thesys brand link

Why

Shared marketing chrome performed avoidable client hydration, animation-library work, API fetching, and repeated React renders around the first interaction.

Impact

This is the shared-interaction slice of #879. It reduces the amount of main-thread work around navigation and pointer input while preserving the marketing layout and theme behavior.

Validation

• pnpm --dir docs types:check
• focused ESLint
• staged diff integrity check
• desktop and light/dark browser QA in the combined optimized build

Tradeoffs

• the header displays the existing fallback star count instead of fetching a live value
• accordion and mobile-menu exit behavior is simpler without AnimatePresence

Supersedes the shared interaction portion of #879.