Put the USB kiosk in the sidebar next to the parts kiosk

The kiosk route lives outside AppLayout, so nothing linked to it - a full-screen
page with no way in from the app is a page nobody finds. It joins the Displays
section beside Parts Kiosk, TV Slideshow and the Shopfloor Dashboard, gated on
the route existing so a build without the USB plugin does not advertise it.

frontend/src/views/AppLayout.vue

@@ -34,6 +34,8 @@
         <a v-if="hasRoute('/tv')" :href="withBase('/tv')" target="_blank" class="external-link">TV Slideshow</a>
         <a v-if="hasRoute('/parts-kiosk')" :href="withBase('/parts-kiosk')"
            target="_blank" class="external-link">Parts Kiosk</a>
+        <a v-if="hasRoute('/usb-kiosk')" :href="withBase('/usb-kiosk')"
+           target="_blank" class="external-link">USB Kiosk</a>
 
         <router-link v-if="authStore.isAdmin" to="/settings">Settings</router-link>
       </nav>
@@ -136,6 +138,7 @@ const hasRoute = (path) => stagedRoutePaths.has(path)
 const showShopfloor = hasRoute('/shopfloor')
   && (hasRoute('/notifications') || hasRoute('/calendar'))
 const showDisplays = showShopfloor || hasRoute('/tv') || hasRoute('/parts-kiosk')
+  || hasRoute('/usb-kiosk')
 const routeViewKey = computed(() =>
   route.path.startsWith('/settings') ? '/settings' : route.path
 )