docs: document on-device message translation

Add the translation feature to the landing page (Newest July 2026
prose + comparison-table row) and the README custom-features table.

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

README.md

@@ -524,6 +524,7 @@ All custom code lives in `src/app/` on the `lotus` branch of `code.lotusguild.or
 | **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 |
 | **Inline media embeds** | `src/app/utils/videoEmbed.ts`, `src/app/components/url-preview/{UrlPreviewCard,UrlPreview.css}.tsx` | Media links play/render **in place** behind a click-to-play **facade** (homeserver `og:image` thumbnail; third-party iframe mounts only on Play). 16 providers: video (YouTube/Shorts, Vimeo, Dailymotion, Streamable, Twitch, Loom, Kick), audio (Spotify, SoundCloud, Apple Music, Tidal), self-resizing posts (X/Twitter, Instagram, Reddit, Bluesky). TikTok short links resolve via CORS `oEmbed`; posts self-size via origin-scoped `postMessage`. Sandbox omits `allow-top-navigation`; previews capped at 6/msg. Setting `inlineMediaEmbeds`. **CSP:** every embed host is enumerated in the desktop Tauri `frame-src` (`cinny-desktop/tauri.conf.json`) **and** the deployed web nginx `frame-src` allowlist on LXC 106 (`/etc/nginx/sites-available/cinny` — hand-maintained; the wildcard `frame-src 'self' https:` in this repo's `cinny/nginx.conf` is the looser fallback) |
+| **On-device message translation** | `src/app/features/room/message/`, `src/app/hooks/useMessageTranslation.ts`, `src/app/state/settings.ts` | "Translate" button on foreign-language messages renders the translation inline with a "Translated from <lang> · Show original" toggle + optional auto-translate mode. Runs **100% on-device** via the browser's built-in Translator API (Chromium: Chrome/Edge + Lotus desktop app) — message text never leaves the device and never reaches any cloud translation service (Google/DeepL/Microsoft), so it works in **E2EE rooms** without weakening encryption. Target language in Settings → General (default English). Feature-detected — gracefully hidden where unsupported (Firefox/Safari/mobile) |
 | **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 |