docs: document desktop features (Tier A + B) across catalog/README/TODO

- LOTUS_FEATURES.md: new "Desktop App Features" section (+ TOC) covering all
  desktop capabilities — no-sleep, jump list, thumbbar, SMTC, network awareness,
  rich notifications, Focus Assist, window chrome, update toast, toolbar reorder,
  draft indicator, recursive folder DnD.
- README.md: "Desktop-Specific Features" bullets under the Desktop App section.
- LOTUS_TODO.md: P5-35/41/56 → [~] IMPLEMENTED (Tier B); P5-48 → [~] (recursive
  folder upload; .lnk/Send-To scoped-out with rationale).

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

README.md

@@ -139,6 +139,20 @@ When you first run the installer on Windows, you may see a popup that says **"Wi
 
 After the first install, automatic in-app updates handle all future versions — you will not see this prompt again for updates.
 
+### Desktop-Specific Features
+
+Beyond the web client, the desktop app adds native OS integration (Windows-focused; graceful no-ops elsewhere). See [`LOTUS_FEATURES.md`](./LOTUS_FEATURES.md#desktop-app-features) for detail.
+
+- **Native rich notifications** — Windows toasts you can click to open the room or reply to inline, right from the toast.
+- **Focus Assist sync** — Lotus silences its own notifications while Windows Focus Assist / Quiet Hours is on.
+- **Windows Jump List** — right-click the taskbar icon for quick access to your most-active rooms.
+- **Taskbar call controls** — Mute / Deafen / End Call buttons on the taskbar thumbnail during a call, plus call status in the volume flyout (SMTC).
+- **Stays awake in calls** — the system won't sleep or dim during a voice/video call.
+- **Network awareness** — reconnects promptly when Windows connectivity changes.
+- **Custom window chrome** (opt-in) — a Lotus-styled title bar in place of the OS one.
+- **Recursive folder drag-drop** — drop a whole folder onto the composer to upload everything inside it.
+- **Automatic background updates** with a one-click update toast.
+
 ---
 
 ## For Developers