Invoke Secure Backup flow inside the app when requested by HS

If the Secure Backup required mode is set the client `.well-known` file, then
this will ensure that everyone already inside the app is required to complete
setup matching that policy.

Fixes https://github.com/vector-im/element-web/issues/14954

src/@types/global.d.ts

@@ -27,10 +27,12 @@ import {ModalManager} from "../Modal";
 import SettingsStore from "../settings/SettingsStore";
 import {ActiveRoomObserver} from "../ActiveRoomObserver";
 import {Notifier} from "../Notifier";
+import type {Renderer} from "react-dom";
 
 declare global {
     interface Window {
         Modernizr: ModernizrStatic;
+        matrixChat: ReturnType<Renderer>;
         mxMatrixClientPeg: IMatrixClientPeg;
         Olm: {
             init: () => Promise<void>;