fix(ui): use a grid icon for Customize Dashboard

The settings icon is a circle with radiating spokes, which reads as a
sun/light-mode toggle rather than a dashboard control. Swap it for the
grid icon, the standard dashboard-layout affordance.

templates/library_switcher.templ

@@ -47,7 +47,7 @@ templ DashboardActions() {
 		class="icon-btn"
 		title="Customize Dashboard"
 	>
-		@Icon("settings", "h-5 w-5")
+		@Icon("grid", "h-5 w-5")
 	</button>
 	<button
 		data-action="reload-page"