docs: Slack-style per-thread notifications (P4-1)

Landing: thread row + prose note the participating-default notifications with
per-thread All/Mentions/Mute. README: Lotus Cinny threads row extended.

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

README.md

@@ -521,7 +521,7 @@ All custom code lives in `src/app/` on the `lotus` branch of `code.lotusguild.or
 | **Document title unread count** | `src/app/pages/client/ClientNonUIFeatures.tsx` | Tab title updates to `(N) Lotus Chat` for mentions, `· Lotus Chat` for unreads, `Lotus Chat` when clear |
 | **Message draft persistence** | `src/app/features/room/RoomInput.tsx` | Unsent messages survive page reload via `localStorage` (`draft-msg-<roomId>`). Jotai in-memory atom remains the primary store; localStorage used as fallback on reload. Cleared on send |
 | **PiP position persistence + snap** | `src/app/components/CallEmbedProvider.tsx` | PiP position saved to `localStorage` on drag end; restored on next PiP enter (clamped to viewport). Double-click snaps to nearest corner with 180ms CSS transition |
-| **Threads (P3-8)** | `src/app/features/room/thread/`, `state/room/thread.ts`, `hooks/useThreadSummary.ts` | Full m.thread support: side panel (own composer, per-thread drafts), "N replies" unread chips on roots, threaded receipts; SDK `threadSupport` on, markAsRead unthreaded. Replies no longer render inline |
+| **Threads (P3-8 + P4-1)** | `src/app/features/room/thread/`, `state/room/thread.ts`, `utils/threadNotifications.ts`, `hooks/useRoomsListener.ts` | Full m.thread support: side panel (own composer, per-thread drafts), "N replies" unread chips, threaded receipts; SDK `threadSupport` on, markAsRead unthreaded; replies no longer render inline. **Slack-style notifications**: default = participating-only, per-thread All/Mentions/Mute in `io.lotus.thread_notifications` account data; muted threads subtracted from room badges client-side |
 | **KaTeX math + encrypted-search cache + session hardening + crypto diagnostics** | `utils/{mathParse,searchCache,cryptoDiagLog}.ts`, `state/sessions.ts`, `LOTUS_E2EE_INVESTIGATION.md` | July 2026 batch: `$…$`/`$$…$$` + `data-mx-maths` via lazy KaTeX; opt-in IndexedDB search index for E2EE rooms (wiped on logout); atomic `cinny_session_v1` blob + cross-tab logout sync; KE-1→4 diagnostics capture card in Developer Tools |
 | **Desktop app (Tauri)** | `cinny-desktop` → `src-tauri/src/native/*.rs`, `src-tauri/src/lib.rs`; cinny `src/app/hooks/useTauri*.ts`, `src/app/components/TauriDesktopFeatures.tsx` | Tauri v2 native shell: rich WinRT toast notifications (click → open room, inline quick reply), Windows Focus Assist → DND sync, taskbar Jump List of recent rooms, taskbar thumbnail + volume-flyout call controls (mute/deafen/end), no-sleep during calls, network-change awareness (`mx.retryImmediately`), opt-in TDS window chrome, recursive folder drag-drop, auto-update toast. Windows-native pieces compile in CI (Gitea `windows` runner + GitHub `windows-latest`); detail in cinny `LOTUS_FEATURES.md` → Desktop App Features |
 | **LiveKit codec config** | `/etc/livekit/config.yaml` (LXC 151) | `enabled_codecs`: VP8, H264, VP9, Opus, RED for better quality and redundancy |