Use false instead of null for empty session

The caching layer of Nuxt assumes no entry exists if it's nullish.  This
causes null to be treated as if the resource needs to be fetched.  Use
false instead.

composables/session.ts

@@ -1,6 +1,6 @@
 export const useAccountSession = () => useFetch(
 	"/api/auth/session",
 	{
-		transform: (input) => input === undefined ? null : input,
+		transform: (input) => input === undefined ? false : input,
 	}
 );