Redesign the public site around the product

[debpalash]

What changed

• replaces the long marketing page with one focused install path
• uses the shipped interface as the primary product proof
• reduces the page to three plain product principles and one privacy boundary
• keeps Windows/WSL secondary and preserves technical requirements
• removes gradients, glass panels, card grids, tab UI, and the autoplay tour
• adds responsive mobile layout, visible focus states, and accessible copy controls

Verification

• npm run check (0 errors, warnings, or hints)
• npm run build
• python -m unittest tests.test_bootstrap -v (9 passed, 1 skipped: PowerShell unavailable)
• bash scripts/check-release.sh
• Playwright at 1440px and 375px: no horizontal overflow; disclosure, clipboard, and keyboard focus verified