feat(mobile): self-update dialog with verified APK download and install (M5)

Checks the server for a newer release at most every 6 hours and on
demand in Profile, shows release notes, downloads the APK with progress,
verifies SHA-256 in 1 MB chunks and hands it to the system installer.
Updates below min_supported cannot be dismissed.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

packages/core/src/auth.ts

@@ -101,6 +101,11 @@ export class AuthSession {
     return this.current;
   }
 
+  /** Текущий access-токен — для запросов мимо `client` (загрузка файлов на Android). */
+  get accessToken(): string | null {
+    return this.access;
+  }
+
   /** Подписка на смену состояния; возвращает функцию отписки. */
   subscribe(fn: (s: AuthState) => void): () => void {
     this.listeners.add(fn);