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/hooks/useTauriSmtc.ts

@@ -0,0 +1,38 @@
+import { useEffect } from 'react';
+import { useAtomValue } from 'jotai';
+import { callEmbedAtom } from '../state/callEmbed';
+import { useCallControlState } from '../plugins/call';
+import { invokeTauri, useTauriEvent } from './useTauri';
+
+/**
+ * P5-43 — expose the active call to the Windows System Media Transport Controls
+ * (the volume-flyout / media overlay). Mirrors the call-embed atom (undefined =
+ * no active call) and the current mic state onto the native
+ * `set_smtc_call_state` command, and translates SMTC button presses back into
+ * call actions:
+ *   - Play/Pause (`smtc-action` → `mute`) toggles the microphone.
+ *   - Stop (`smtc-action` → `end`) hangs up the call.
+ * No-op in the browser (the native command and events only fire under Tauri).
+ */
+type SmtcAction = { action: 'mute' | 'end' };
+
+export function useTauriSmtc(): void {
+  const callEmbed = useAtomValue(callEmbedAtom);
+  // `microphone` reflects mic-enabled; muted is its inverse while in a call.
+  const { microphone } = useCallControlState(callEmbed?.control);
+  const active = callEmbed !== undefined;
+  const muted = active && !microphone;
+
+  useEffect(() => {
+    invokeTauri('set_smtc_call_state', { active, muted });
+  }, [active, muted]);
+
+  useTauriEvent<SmtcAction>('smtc-action', ({ action }) => {
+    if (!callEmbed) return;
+    if (action === 'mute') {
+      callEmbed.control.toggleMicrophone().catch(() => undefined);
+    } else if (action === 'end') {
+      callEmbed.hangup().catch(() => undefined);
+    }
+  });
+}