fix(threads): harden threads list after review

Address findings from 3 review agents on the Threads list panel:

- Last-activity accuracy (SDK): sort key and the "last reply <time>"
  label now use thread.replyToEvent.getTs() (server bundle latest_event)
  instead of lastReply(), which returns the ROOT time until each thread's
  replies lazily paginate (or permanently on fetch error). Applied to the
  hook signature too.

- Live-refresh completeness (correctness): the useRoomThreads signature
  now includes thread.length and the root event's replacingEventId, so a
  mid-thread redaction (reply count) and a root-message edit (row snippet)
  refresh the row live instead of going stale.

- a11y: the row's aria-label was the button's whole accessible name,
  hiding the snippet/count/unread from screen readers. It now describes
  the thread ("Open thread by <name>, unread, N replies, last reply ..").

- Unread badge: replaced the bare green dot (Success = the mention color)
  with the app-wide UnreadBadge, using the Highlight count so mentions
  render red and ordinary unread renders secondary, matching room-nav.

- Hover/focus affordance: the clickable row moved its inline styles to a
  css class with token-based :hover / :active backgrounds.

- Participant pile now also includes the last replier from the bundle.

- Stabilized the panel's onClose/onOpenThread with useCallback so its
  Escape listener isn't re-subscribed every Room render. Added
  filter->sort pipeline + all/participating immutability tests.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app/features/room/Room.tsx

@@ -70,6 +70,17 @@ export function Room() {
     ),
   );
 
+  // Stable handlers for the threads-list panel so its document-level Escape
+  // listener isn't torn down and re-added on every Room re-render.
+  const closeThreadsList = useCallback(() => setThreadsListOpen(false), [setThreadsListOpen]);
+  const openThreadFromList = useCallback(
+    (threadId: string) => {
+      setActiveThreadId(threadId);
+      setThreadsListOpen(false);
+    },
+    [setActiveThreadId, setThreadsListOpen],
+  );
+
   const callView = callEmbed?.roomId === room.roomId || room.isCallRoom() || callMembers.length > 0;
 
   // The content panels (thread / media gallery / widgets) are mutually exclusive
@@ -190,11 +201,8 @@ export function Room() {
             <ThreadsListPanel
               key={room.roomId}
               room={room}
-              onClose={() => setThreadsListOpen(false)}
-              onOpenThread={(threadId) => {
-                setActiveThreadId(threadId);
-                setThreadsListOpen(false);
-              }}
+              onClose={closeThreadsList}
+              onOpenThread={openThreadFromList}
             />
           </>
         )}