feat(ui): tone-based icon palette for app-tile, dark-mode aware

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>

core/Support/helpers/ui.php

@@ -827,6 +827,7 @@ function appTile(array $options = []): void
         'label' => '',
         'count' => null,
         'icon' => 'bi bi-grid-1x2',
+        'iconTone' => null,
         'iconBg' => null,
         'iconColor' => null,
         'class' => '',