feat(chat): add transient presence flash and 5s reconnect grace period

.github/instructions/TODO.md

@@ -2,6 +2,16 @@
 
 > Completed tasks moved to [DONE](./DONE.md). Remaining tasks in [BACKLOG](./BACKLOG.md).
 
+## Chat improvements (remaining)
+
+- [ ] Manual smoke: viewer join/leave shows a 3s flash (not a chat row); reconnect <5s shows no duplicate; admin chat-log table has no system rows
+
+## Playout improvements (remaining)
+
+- [ ] Test in Firefox: live playback, rebuffer/recovery, chat sync; record quirks in `docs/STREAMING.md`
+- [ ] Rebuild + run playout; confirm `playlist.m3u8` lists ~12 segments at 2s each
+- [ ] Manual: verify viewer latency and cache-hit behavior after the change
+
 ## Setup phases remaining
 
 ### Phase 5: complete manual Cloudflare and external-service setup