Dan Mode: pure white backgrounds, electric blue text (#0000ff), nuclear
yellow accents (#ffff00), hot magenta borders (#ff00ff), red labels,
glowing box-shadows. Maximum saturation. Hostile to human vision by design.
Theme toggle now cycles light → dark → dan → light (icons: 🌙😎☀️).
PICO_CSS.md: documents [role=button] color clobber, palette scoping rules,
and theme toggling pattern for future reference.
Fix: palette overrides now use @media(prefers-color-scheme:light) +
[data-theme=light] only — no more :root:not([data-theme=dark]) which
incorrectly matched OS-dark with no attribute set.
Feat: theme toggle button in nav (🌙/☀️), persisted to localStorage,
applied via data-theme attribute on <html>. Respects OS preference on
first visit.
