fix(a11y): thread chip says it opens the thread, and whether it's unread/muted (#179)

The "N replies · <time>" chip under a thread root was named only by its
visible text, so a screen reader never said it opens the thread, and the
unread dot / muted bell were visual-only. Its accessible name is now the
visible text first (WCAG 2.5.3) plus "view thread", "unread replies" and
"muted" as applicable, e.g. "1 reply · 12:16 PM, view thread".

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PPmy3tPq869XDW4njjVaKA

src/app/features/room/thread/ThreadSummary.tsx

@@ -19,6 +19,18 @@ export function ThreadSummary({ rootEvent, room, onOpen }: ThreadSummaryProps) {
 
   const { count, latestTs } = summary;
   const latestStr = latestTs !== undefined ? format(latestTs) : undefined;
+  const visibleText = `${count === 1 ? '1 reply' : `${count} replies`}${latestStr ? ` · ${latestStr}` : ''}`;
+  // #179: the chip was named only by its visible text, so a screen reader never
+  // heard that it opens the thread, nor about the unread dot / muted bell. Keep
+  // the visible text first (WCAG 2.5.3, label in name) and add the rest.
+  const ariaLabel = [
+    visibleText,
+    'view thread',
+    unread > 0 ? 'unread replies' : undefined,
+    mode === ThreadNotificationMode.Mute ? 'muted' : undefined,
+  ]
+    .filter(Boolean)
+    .join(', ');
 
   return (
     <Box style={{ marginTop: config.space.S200 }}>
@@ -26,6 +38,7 @@ export function ThreadSummary({ rootEvent, room, onOpen }: ThreadSummaryProps) {
         variant="SurfaceVariant"
         radii="300"
         className={MobileTouchTarget}
+        aria-label={ariaLabel}
         before={<Icon size="50" src={Icons.Thread} />}
         after={
           unread > 0 ? <Badge variant="Success" fill="Solid" radii="Pill" size="200" /> : undefined
@@ -35,10 +48,7 @@ export function ThreadSummary({ rootEvent, room, onOpen }: ThreadSummaryProps) {
           if (threadId) onOpen(threadId);
         }}
       >
-        <Text size="T200">
+        <Text size="T200">{visibleText}</Text>
-          {count === 1 ? '1 reply' : `${count} replies`}
-          {latestStr ? ` · ${latestStr}` : ''}
-        </Text>
         {mode === ThreadNotificationMode.Mute && <Icon size="50" src={Icons.BellMute} />}
       </Chip>
     </Box>