feat(desktop): Tier A desktop features — web side (P5-46/36/44/43/49/47/55/57)

Web half of the desktop feature wave. A shared bridge (`hooks/useTauri.ts`:
invokeTauri/isTauri/useTauriEvent) backs per-feature hooks that no-op in the
browser and drive the native Tauri commands (compiled in cinny-desktop):

- P5-46 useTauriCallPower — hold system awake while a call is active.
- P5-36 useTauriJumpList — Windows jump list of recent rooms → matrix: deep links.
- P5-44 useTauriThumbbar — taskbar Mute/Deafen/End; events toggle mic/sound/hangup.
- P5-43 useTauriSmtc — SMTC call state + button events.
- P5-49 useTauriNetwork — react to native network-change → mx.retryImmediately().
- P5-47 window chrome — opt-in `customWindowChromeAtom` + TDS `TitleBar`; DesktopChrome
  wrapper in App.tsx (zero layout impact when off) + a desktop-only settings toggle.
- P5-55 composer toolbar drag-reorder (settings order[] + pragmatic-drag-and-drop).
- P5-57 DraftIndicator — subtle "draft saved" cue in the composer.

Client-scoped hooks mount via TauriDesktopFeatures in ClientNonUIFeatures; window
chrome mounts at App level. Gates: tsc/eslint/prettier clean, build OK, 556 tests.

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

src/app/components/TauriDesktopFeatures.tsx

@@ -0,0 +1,21 @@
+import { useTauriCallPower } from '../hooks/useTauriCallPower';
+import { useTauriJumpList } from '../hooks/useTauriJumpList';
+import { useTauriThumbbar } from '../hooks/useTauriThumbbar';
+import { useTauriSmtc } from '../hooks/useTauriSmtc';
+import { useTauriNetwork } from '../hooks/useTauriNetwork';
+
+/**
+ * Mounts the client-scoped native desktop feature hooks (call/room aware). Each
+ * `useTauri*` hook no-ops in the browser (guards on `isTauri`), so this is safe
+ * to render unconditionally. Rendered once by `ClientNonUIFeatures`. App-level
+ * desktop features (window chrome) live in `App.tsx` instead, so they work
+ * before login.
+ */
+export function TauriDesktopFeatures(): null {
+  useTauriCallPower(); // P5-46 no-sleep during calls
+  useTauriJumpList(); // P5-36 Windows jump list of recent rooms
+  useTauriThumbbar(); // P5-44 taskbar thumbnail toolbar (mute/deafen/end)
+  useTauriSmtc(); // P5-43 system media transport controls
+  useTauriNetwork(); // P5-49 network-change awareness → sync retry
+  return null;
+}