perf+fix: debounce seq persistence + role changes, null-clear stale peer state

- server: SET_PEER_ROLE now uses the same per-room 500ms debounce as
  SET_CONTROL_MODE (M-4), preventing a buggy/malicious host from
  thrashing the room's UI with rapid promote/demote bursts.
- server: PEER_STATUS relay treats explicit null as 'clear' for
  tabTitle/mediaTitle/currentTime, so the tab-close heartbeat actually
  zeroes out stale state on other peers instead of being silently
  preserved by the clamp fallback.
- background: _persistLastSeq is now trailing-debounced (500ms),
  cutting storage.session IPC writes from one-per-relayed-event to
  one-per-quiet-window in active rooms.
- locales: add missing TOAST_ID_REGENERATED to all 14 non-English
  locales (was blocking locale coverage test on main).
- test: H-1 force-sync demote test now waits out the debounce window
  to reflect real-world UI timing (a host cannot promote, run a
  force-sync, and demote inside 500ms).

scripts/test-server-ws.mjs

@@ -245,6 +245,9 @@ try {
     await w(ho,'force_sync_prepare'); await w(hg,'force_sync_prepare');
     ho._m.length = hc._m.length = hg._m.length = 0;
     // owner demotes the co-host mid-flight — the EXECUTE must still go through.
+    // Wait out the per-room role-change debounce (M-4) so this demote broadcasts:
+    // in real usage the host can't promote, run a force-sync, and demote inside 500ms.
+    await new Promise(r => setTimeout(r, 550));
     s(ho,'set_peer_role',{peerId:'cohost',controller:false});
     await w(hc,'control_mode');
     ho._m.length = hc._m.length = hg._m.length = 0;