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>

pages/admin/settings/index(default).phtml

@@ -19,72 +19,63 @@
       'href' => 'admin/settings/general',
       'label' => t('General'),
       'icon' => 'bi bi-sliders',
-      'iconBg' => '#e0ecff',
-      'iconColor' => '#2563eb',
+      'iconTone' => 'blue',
       'tooltip' => t('App title, language, user creation defaults'),
     ]);
     appTile([
       'href' => 'admin/settings/account-access',
       'label' => t('Account access'),
       'icon' => 'bi bi-shield-lock',
-      'iconBg' => '#ede9fe',
-      'iconColor' => '#7c3aed',
+      'iconTone' => 'violet',
       'tooltip' => t('Registration, sessions, login persistence'),
     ]);
     appTile([
       'href' => 'admin/settings/user-lifecycle',
       'label' => t('User lifecycle'),
       'icon' => 'bi bi-arrow-repeat',
-      'iconBg' => '#fee2e2',
-      'iconColor' => '#b91c1c',
+      'iconTone' => 'red',
       'tooltip' => t('Inactivity deactivation and deletion policy'),
     ]);
     appTile([
       'href' => 'admin/settings/audit',
       'label' => t('Audit log'),
       'icon' => 'bi bi-journal-text',
-      'iconBg' => '#fff7ed',
-      'iconColor' => '#c2410c',
+      'iconTone' => 'orange',
       'tooltip' => t('System audit log enable and retention'),
     ]);
     appTile([
       'href' => 'admin/settings/telemetry',
       'label' => t('Telemetry'),
       'icon' => 'bi bi-graph-up',
-      'iconBg' => '#ecfdf5',
-      'iconColor' => '#047857',
+      'iconTone' => 'green',
       'tooltip' => t('Frontend telemetry collection and event allowlist'),
     ]);
     appTile([
       'href' => 'admin/settings/email',
       'label' => t('Email'),
       'icon' => 'bi bi-envelope',
-      'iconBg' => '#fef3c7',
-      'iconColor' => '#d97706',
+      'iconTone' => 'amber',
       'tooltip' => t('SMTP connection and sender details'),
     ]);
     appTile([
       'href' => 'admin/settings/api',
       'label' => t('API'),
       'icon' => 'bi bi-key',
-      'iconBg' => '#d1fae5',
-      'iconColor' => '#059669',
+      'iconTone' => 'emerald',
       'tooltip' => t('API token policy and CORS allowlist'),
     ]);
     appTile([
       'href' => 'admin/settings/sso',
       'label' => t('Microsoft SSO'),
       'icon' => 'bi bi-microsoft',
-      'iconBg' => '#dbeafe',
-      'iconColor' => '#0891b2',
+      'iconTone' => 'cyan',
       'tooltip' => t('Shared Microsoft Entra ID credentials'),
     ]);
     appTile([
       'href' => 'admin/settings/branding',
       'label' => t('Branding'),
       'icon' => 'bi bi-palette',
-      'iconBg' => '#fce7f3',
-      'iconColor' => '#be185d',
+      'iconTone' => 'pink',
       'tooltip' => t('App logo and favicon'),
     ]);
     ?>