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/utils/threadList.test.ts

@@ -67,10 +67,13 @@ test('sortThreads breaks ties deterministically by id', () => {
   );
 });
 
-test('filterThreads / sortThreads do not mutate input', () => {
-  const input = [t('a', 100), t('b', 300)];
+test('filterThreads / sortThreads do not mutate input (all/participating branches)', () => {
+  const input = [t('a', 100, 1, true), t('b', 300, 0, false)];
   const before = input.map((x) => x.id);
+  filterThreads(input, 'all');
+  filterThreads(input, 'participating');
   filterThreads(input, 'unread');
+  sortThreads(input, 'recent');
   sortThreads(input, 'oldest');
   assert.deepEqual(
     input.map((x) => x.id),
@@ -78,6 +81,15 @@ test('filterThreads / sortThreads do not mutate input', () => {
   );
 });
 
+test('filter → sort pipeline composes (unread + recent)', () => {
+  const input = [t('a', 100, 2), t('b', 300, 0), t('c', 200, 1)];
+  const out = sortThreads(filterThreads(input, 'unread'), 'recent');
+  assert.deepEqual(
+    out.map((x) => x.id),
+    ['c', 'a'],
+  );
+});
+
 test('isThreadFilter / isThreadSort accept valid and reject junk', () => {
   assert.equal(isThreadFilter('all'), true);
   assert.equal(isThreadFilter('unread'), true);