feat(ui): fix queue item count badge positioning

Previously this badge, floating over the queue menu button next to the invoke button, was rendered within the existing layout. When I initially positioned it, the app layout interfered - it would extend into an area reserved for a flex gap, which cut off the badge.

As a (bad) workaround, I had shifted the whole app down a few pixels to make room for it. What I should have done is what I've done in this commit - render the badge in a portal to take it out of the layout so we don't need that extra vertical padding.

Sleekified some styling a bit too.

invokeai/frontend/web/src/features/queue/components/QueueControls.tsx

@@ -11,7 +11,7 @@ import { QueueActionsMenuButton } from './QueueActionsMenuButton';
 const QueueControls = () => {
   const isPrependEnabled = useFeatureStatus('prependQueue');
   return (
-    <Flex w="full" position="relative" borderRadius="base" gap={2} pt={2} flexDir="column">
+    <Flex w="full" position="relative" borderRadius="base" gap={2} flexDir="column">
       <ButtonGroup size="lg" isAttached={false}>
         {isPrependEnabled && <QueueFrontButton />}
         <InvokeQueueBackButton />