fix: improve badge text color contrast for WCAG AA compliance
Added CSS custom properties --type-{name}-text for each article type with appropriate text colors per theme:
- Dark mode: all types use black text (#000000) for sufficient contrast
- Light mode: tech and photo types use white text (#ffffff), life/quote/link use black text (#000000)
Updated article-header.html and article-card.html to use color: var(--type-{name}-text) instead of hardcoded text-white class.
Improves contrast ratios:
- Quote type dark mode: 1.34:1 → 15.66:1 (white on #00ff88 was failing WCAG AA)
- All other types now pass 4.5:1 minimum for WCAG AA small text
