Use LayoutType from is_mobile in actions/app (#24863)

app/javascript/mastodon/actions/app.ts

@@ -1,10 +1,11 @@
 import { createAction } from '@reduxjs/toolkit';
+import type { LayoutType } from '../is_mobile';
 
 export const focusApp = createAction('APP_FOCUS');
 export const unfocusApp = createAction('APP_UNFOCUS');
 
 type ChangeLayoutPayload = {
-  layout: 'mobile' | 'single-column' | 'multi-column';
+  layout: LayoutType;
 };
 export const changeLayout =
   createAction<ChangeLayoutPayload>('APP_LAYOUT_CHANGE');