Redesign: RFC-minimal aesthetic with custom landing page

Inspired by promptext design system:
- Zero border radius (sharp edges throughout)
- Monochrome contrast (black/white, no color accents)
- 8px grid system (granular spacing control)
- Elegant sidebar with left border on active items
- Link underlines with offset for readability
- Inline code with borders instead of backgrounds
- Enhanced focus states with glow effects
- Custom landing page with feature showcase
- Glassmorphism navigation with backdrop blur

Design philosophy: Technical, RFC-spec aesthetic.
High contrast. Purpose over decoration.

Author: 1broseidon