♿️(frontend) add screen reader announcer store

create shared state for screen reader announcements.

src/frontend/src/stores/screenReaderAnnouncer.ts

@@ -0,0 +1,33 @@
+import { proxy } from 'valtio'
+
+type Politeness = 'polite' | 'assertive'
+
+type ScreenReaderAnnouncement = {
+  message: string
+  politeness: Politeness
+  id: number
+}
+
+type ScreenReaderAnnouncerState = {
+  announcement: ScreenReaderAnnouncement
+}
+
+export const screenReaderAnnouncerStore = proxy<ScreenReaderAnnouncerState>({
+  announcement: {
+    message: '',
+    politeness: 'polite',
+    id: 0,
+  },
+})
+
+export const announceToScreenReader = (
+  message: string,
+  politeness: Politeness = 'polite'
+) => {
+  screenReaderAnnouncerStore.announcement = {
+    message,
+    politeness,
+    id: screenReaderAnnouncerStore.announcement.id + 1,
+  }
+}
+