Serve avatars from site's own /imaging endpoint instead of habbo.com

- Change default public imager URL from habbo.com to /imaging
- /imaging and /api/imaging/avatar now proxy from upstream (habbo.com) instead of redirecting
- Add resolveUpstreamBase() to separate public URL from upstream URL
- Update admin settings default and description

src/lib/services/site-settings.ts

@@ -3,7 +3,7 @@ import { redis } from "@/lib/redis";
 
 const DEFAULTS: Record<string, string> = {
 	hotel_name: "Atom",
-	habbo_imaging_url: "https://www.habbo.com/habbo-imaging/avatarimage",
+	habbo_imaging_url: "/imaging",
 	logo_url: "",
 	nitro_client_url: "",
 };