Redesign: Linear design system with humanized text

- Apply Linear.app design system across all pages
- Dark-mode-native palette (#08090a canvas)
- Inter Variable with cv01/ss03 OpenType features
- Semi-transparent white borders (rgba 0.05-0.08)
- Weight 510 signature emphasis throughout
- Brand indigo (#5e6ad2) for CTAs only
- JetBrains Mono for code blocks
- Humanizer pass on all article text
- Security sweep: no personal info leaks

Author: cappy-dev