Disable tap highlight on interactive elements

Remove the blue/gray selection overlay that appears when tapping
buttons, links, sidebar items and other interactive elements on
mobile devices.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/src/styles/Layout.css

@@ -44,6 +44,26 @@ body {
   padding: 0;
 }
 
+/* Disable tap highlight on all interactive elements */
+button,
+a,
+input,
+select,
+textarea,
+label,
+[role="button"],
+[tabindex],
+.sidebar,
+.sidebar *,
+.nav-item,
+.order-card,
+.toggle-modern,
+.page-tab-btn,
+.admin-tabs-slider *,
+.page-tabs-slider * {
+  -webkit-tap-highlight-color: transparent;
+}
+
 /* Page header slider - rounded pill style (like admin panel) */
 .page-tabs-slider,
 .admin-tabs-slider {