feat(a11y): screen-reader announcements for call events (#168)

A visually hidden aria-live=polite region (rendered by CallEmbedProvider so it
outlives the embed) announces joins/leaves — batched over 1.5 s: 'alice
joined', 'alice and bob joined', '3 people joined' — your own mute/unmute,
deafen/undeafen and screenshare start/stop, and 'Call ended'. Nothing visible,
nothing audible for anyone else, no setting. Verified headless by observing
the region: bob joined → You are muted → … → bob left → Call ended.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PPmy3tPq869XDW4njjVaKA

src/app/components/CallEmbedProvider.tsx

@@ -47,6 +47,9 @@ import { previewRingtone, startRingtone, unlockRingtoneAudio } from '../utils/ri
 import { useCallMembersChange, useCallSession } from '../hooks/useCall';
 import { useCallJoinLeaveSounds } from '../hooks/useCallJoinLeaveSounds';
 import { useCallPolicyRevokedToast } from '../hooks/useCallPolicyRevokedToast';
+import { useCallAnnouncements } from '../hooks/useCallAnnouncements';
+import { callAnnouncementAtom } from '../state/callAnnouncement';
+import { SrOnly } from '../features/call-status/styles.css';
 import { useCallHotkeys } from '../hooks/useCallHotkeys';
 import { useAfkAutoMute } from '../hooks/useAfkAutoMute';
 import { useCallQuality } from '../hooks/useCallQuality';
@@ -676,6 +679,16 @@ function IncomingCallListener({ callEmbed, joined }: IncomingCallListenerProps)
   );
 }
 
+// [Gitea #168] Lives outside the embed so "Call ended" is still announced.
+function CallAnnouncementRegion() {
+  const announcement = useAtomValue(callAnnouncementAtom);
+  return (
+    <span className={SrOnly} role="status" aria-live="polite" aria-atomic="true">
+      {announcement}
+    </span>
+  );
+}
+
 function CallUtils({ embed, joined }: { embed: CallEmbed; joined: boolean }) {
   const setCallEmbed = useSetAtom(callEmbedAtom);
 
@@ -687,6 +700,7 @@ function CallUtils({ embed, joined }: { embed: CallEmbed; joined: boolean }) {
   useAfkAutoMute(joined ? embed : undefined);
   useCallJoinLeaveSounds(embed);
   useCallPolicyRevokedToast(embed, joined);
+  useCallAnnouncements(embed, joined);
   useCallThemeSync(embed);
   useCallQuality(embed);
   useCallHangupEvent(
@@ -1230,6 +1244,7 @@ export function CallEmbedProvider({ children }: CallEmbedProviderProps) {
   return (
     <CallEmbedContextProvider value={callEmbed}>
       {callEmbed && <CallUtils embed={callEmbed} joined={joined} />}
+      <CallAnnouncementRegion />
       <CallEmbedRefContextProvider value={callEmbedRef}>
         <IncomingCallListener callEmbed={callEmbed} joined={joined} />
         {children}