feat(desktop): add offline cache and verified app updates

Clean release notes in Android and desktop update dialogs. Persist downloaded audio and offline playback events per server and user; add desktop update checks, checksum verification and installer launch.

apps/web/src/main.tsx

@@ -9,7 +9,7 @@ import { I18nextProvider } from 'react-i18next';
 import { App } from './App';
 import { createAppRouter } from './app/router';
 import { applyTheme } from './app/session';
-import { createDesktop, DesktopProvider } from './desktop';
+import { createDesktop, DesktopProvider, desktopFetch } from './desktop';
 
 const LOCALE_KEY = 'pipu.locale';
 
@@ -70,6 +70,7 @@ const session = new AuthSession({
   deviceName: desktop ? 'Pipu / Desktop' : deviceName(),
   baseUrl: desktop?.proxyBase,
   refreshStore: desktop?.refreshStore,
+  fetch: desktop ? desktopFetch : undefined,
 });
 // До первого рендера узнаём, есть ли сессия (refresh-cookie), — guards роутера решают сразу.
 await session.restore();