Fix Nitro client launcher: read the nitro_path setting

The /client launcher read a non-existent `nitro_client_url` setting, so it
always fell through to "No client configured" and the client never launched.
Faithful to AtomCMS's NitroController + nitro.blade.php, build the launch URL
as {nitro_path}/index.html?sso=<ticket> plus the toolbar colour params, via a
shared buildNitroClientUrl helper. The Flash launcher's Nitro fallback used the
same dead key and is fixed too.

src/lib/services/site-settings.ts

@@ -6,7 +6,7 @@ const DEFAULTS: Record<string, string> = {
   hotel_name: "Atom",
   habbo_imaging_url: "https://www.habbo.com/habbo-imaging/avatarimage",
   logo_url: "",
-  nitro_client_url: "",
+  nitro_path: "",
 };
 
 /**