refac: onScroll -> IntersectionObserver for infinite scroll

src/lib/stores/index.ts

@@ -41,6 +41,7 @@ export const showSettings = writable(false);
 export const showArchivedChats = writable(false);
 export const showChangelog = writable(false);
 export const showCallOverlay = writable(false);
+
 export const scrollPaginationEnabled = writable(true);
 export const pageSkip = writable(0);
 export const pageLimit = writable(-1);