feat: add osu skin retrieval functionality and integrate into loading and setup processes

src/lib/global.ts

@@ -22,6 +22,8 @@ export const skins = writable<number | undefined>(undefined);
 export const osuStream = writable<string | undefined>(undefined);
 export const osuBuild = writable<string | undefined>(undefined);
 
+export const currentSkin = writable<string>("");
+
 let updateValues = true;
 launching.subscribe((val) => (updateValues = !val));