fix: low-tail correctness — thread notifs, call audio, OIDC expiry

Verify-then-fix batch of minor bugs; each staged diff reviewed by 2 agents
(both SHIP). Two listed items (N6 receipt-avatar refresh, H10 room-name
length reject) were already handled and left unchanged.

Threads:
- T5: a just-sent reply no longer under-notifies — `participated` also checks
  the local thread timeline for our own events, since the server-bundle
  `hasCurrentUserParticipated` lags.
- T6: a room set to "Mentions & Keywords only" no longer over-notifies Default
  thread replies — new `roomMentionsOnly` gate (behavior-identical when false;
  +4 unit tests).
- T7: thread-mode account-data writes are serialized with content carried
  forward (setAccountData is a bare PUT whose result lags the /sync echo, so
  plain serialization wouldn't stop the lost update); carry only on success.

Calls / audio:
- C-L2: a real incoming ring cancels a lingering Settings ringtone preview.
- C-L3: the ringtone AudioContext is primed on the first page gesture (via the
  always-mounted CallEmbedProvider) so the first ring after a cold load isn't
  silent.
- C-L5: useCallSpeakers depends on a stable boolean, so the tile MutationObserver
  + io.lotus.call_state subscription aren't rebuilt on every membership change.

Crypto:
- F5: the OIDC refresher forwards the freshly-refreshed token expiry
  (passed on the tokens object at runtime) as expiresInMs, so the persisted
  expiresAt no longer goes stale across reloads.

Gates: tsc 0, eslint 0, prettier clean, 860/860 tests, build ok.

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

src/app/utils/ringtones.ts

@@ -29,6 +29,18 @@ const getCtx = (): AudioContext | undefined => {
   }
 };
 
+/**
+ * C-L3 — prime (create + resume) the shared ringtone AudioContext from within a
+ * user gesture. Browsers keep a fresh context suspended until a gesture, and an
+ * incoming-call ring fires with no gesture of its own, so the first ring after a
+ * cold page load could be silent (resume() is async and may not finish before
+ * the notes are scheduled). Call this on any early app gesture so a later ring
+ * plays through an already-running context. Mirrors `unlockCallSounds`.
+ */
+export const unlockRingtoneAudio = (): void => {
+  getCtx();
+};
+
 type Note = {
   freq: number;
   /** Offset from phrase start, in seconds */
@@ -173,6 +185,10 @@ const startSynth = (style: SynthStyle, volume: number, loop: boolean): (() => vo
  * silent. This matches the pre-existing behaviour of the classic ringtone.
  */
 export const startRingtone = (id: RingtoneId, volume: number): (() => void) => {
+  // C-L2 — a real incoming ring supersedes any lingering Settings preview so the
+  // two don't overlap (the preview is otherwise only cleared by its own timer).
+  activePreviewStop?.();
+  activePreviewStop = null;
   if (id === 'none') return () => undefined;
   if (id === 'classic') return startClassic(volume, true);
   return startSynth(id, volume, true);