Prompt the user when key storage is unexpectedly off (#29912)

* Assert that we set backup_disabled when turning off key storage

* Prompt the user when key storage is unexpectedly off

* Playwright tests for the Turn on key storage toast

res/css/_common.pcss

@@ -593,6 +593,7 @@ legend {
 .mx_Dialog
     button:not(
         .mx_EncryptionUserSettingsTab button,
+        .mx_EncryptionCard button,
         .mx_UserProfileSettings button,
         .mx_ShareDialog button,
         .mx_UnpinAllDialog button,

res/css/_components.pcss

@@ -131,6 +131,7 @@
 @import "./views/dialogs/_BugReportDialog.pcss";
 @import "./views/dialogs/_ChangelogDialog.pcss";
 @import "./views/dialogs/_CompoundDialog.pcss";
+@import "./views/dialogs/_ConfirmKeyStorageOffDialog.pcss";
 @import "./views/dialogs/_ConfirmSpaceUserActionDialog.pcss";
 @import "./views/dialogs/_ConfirmUserActionDialog.pcss";
 @import "./views/dialogs/_CreateRoomDialog.pcss";

res/css/structures/_ToastContainer.pcss

@@ -79,6 +79,11 @@ Please see LICENSE files in the repository root for full details.
                 background-color: $primary-content;
             }
 
+            &.mx_Toast_icon_key_storage::after {
+                mask-image: url("@vector-im/compound-design-tokens/icons/settings-solid.svg");
+                background-color: $primary-content;
+            }
+
             &.mx_Toast_icon_labs::after {
                 mask-image: url("$(res)/img/element-icons/flask.svg");
                 background-color: $secondary-content;

res/css/views/dialogs/_ConfirmKeyStorageOffDialog.pcss

@@ -0,0 +1,16 @@
+/*
+Copyright 2025 New Vector Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR GPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE files in the repository root for full details.
+*/
+
+.mx_ConfirmKeyStorageOffDialog {
+    .mx_Dialog_border {
+        width: 600px;
+    }
+
+    .mx_EncryptionCard {
+        text-align: center;
+    }
+}