Adds an iconTone API (blue, violet, red, orange, amber, emerald, cyan,
pink, green, neutral) to appTile() that derives both icon background and
color from a single hue via color-mix(). Light mode keeps the pastel-pill
look; dark mode picks subtle dark-tinted backgrounds with bright accent
icons so tiles read clearly on the dark background.
The existing iconBg/iconColor escape hatch stays for callers that need a
custom hex (admin/stats); the nine settings tiles migrate to iconTone.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>