Update $app/stores page.stuff to use App.Stuff (sveltejs#3686)

* Update $app/stores page.stuff to use App.Stuff

Following sveltejs#3670, `page.stuff` from `$app/stores` should use `App.Stuff` instead of the old `Record<string, any>`

* Create sharp-beers-know.md

Co-authored-by: Rich Harris <hello@rich-harris.dev>

Author: tmarnet

.changeset/sharp-beers-know.md

@@ -0,0 +1,5 @@
+---
+"@sveltejs/kit": patch
+---
+
+Update $app/stores page.stuff to use App.Stuff

packages/kit/types/ambient-modules.d.ts

@@ -125,7 +125,7 @@ declare module '$app/stores' {
 	export const page: Readable<{
 		url: URL;
 		params: Record<string, string>;
-		stuff: Record<string, any>;
+		stuff: App.Stuff;
 		status: number;
 		error: Error | null;
 	}>;