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>

templates/partials/app-tile.phtml

@@ -5,6 +5,7 @@
  * @var string $label
  * @var string|null $count
  * @var string|null $icon
+ * @var string|null $iconTone
  * @var string|null $iconBg
  * @var string|null $iconColor
  * @var string|null $class
@@ -16,12 +17,16 @@ $href = $href ?? '#';
 $label = $label ?? '';
 $count = $count ?? null;
 $icon = $icon ?? 'bi bi-grid-1x2';
+$iconTone = $iconTone ?? null;
 $iconBg = $iconBg ?? null;
 $iconColor = $iconColor ?? null;
 $class = $class ?? '';
 $tooltip = $tooltip ?? '';
 $tooltipPos = $tooltipPos ?? 'top';
 
+$allowedTones = ['blue', 'violet', 'red', 'orange', 'amber', 'emerald', 'cyan', 'pink', 'green', 'neutral'];
+$resolvedTone = is_string($iconTone) && in_array($iconTone, $allowedTones, true) ? $iconTone : null;
+
 $styleParts = [];
 if ($iconBg) {
   $styleParts[] = '--tile-icon-bg:' . $iconBg;
@@ -35,6 +40,7 @@ $style = $styleParts ? implode(';', $styleParts) . ';' : '';
 <a
   class="app-tile<?php echo $class ? ' ' . $class : ''; // raw-html-ok: internal CSS class from tile config ?>"
   href="<?php e($href); ?>"
+  <?php if ($resolvedTone !== null) : ?>data-tone="<?php e($resolvedTone); ?>"<?php endif; ?>
   <?php if ($style) : ?>style="<?php e($style); ?>"<?php endif; ?>
   <?php if ($tooltip !== '') : ?>data-tooltip="<?php e($tooltip); ?>" data-tooltip-pos="<?php e($tooltipPos); ?>"<?php endif; ?>
 >