Add dark mode with cookie-based persistence and system preference detection
Uses a plain cookie readable by both client JS and server middleware so
the server renders the correct .dark class on <html> without flash.
First-time visitors get an inline nonce script that detects
prefers-color-scheme, sets the cookie, and applies dark mode before
paint. A moon/sun toggle (Alpine.js) lets users override manually.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>