added support for multiple accounts with an account switcher in settings

lib/push/push_registration.dart

@@ -427,6 +427,13 @@ class PushRegistration {
   /// first, then the proxy) with the new token.
   Future<void> onTokenRefresh() => register();
 
+  /// Stops pushes for the active account before another one takes over. The
+  /// app passwords stay valid so switching back can re-register silently.
+  Future<void> deactivate() async {
+    if (DemoMode.active || _nextcloudOrNull == null) return;
+    await unregister();
+  }
+
   /// Full teardown for logout: unregister push, revoke BOTH app passwords
   /// (each authenticated with itself — the endpoint revokes the credential it
   /// is called with), then clear them locally. Ordered so the proxy stops