feat(a11y): add aria-live region to toast notifications

Adds role='status' and aria-live='polite' to the notification
container so screen readers announce status messages.

Fixes WCAG 4.1.3 (Status Messages).

frontend/src/components/misc/Notification.vue

@@ -4,6 +4,8 @@
 		:max="2"
 		:ignore-duplicates="true"
 		class="global-notification"
+		role="status"
+		aria-live="polite"
 	>
 		<template #body="{ item, close }">
 			<!-- FIXME: overlay whole notification with button and add event listener on that button instead -->