Add Optius scraper via its official RSS feed

Optius publishes an RSS feed with region/field filters, so no HTML
scraping is needed. Also move the duplicated slug helper into http.ts
(output unchanged, so existing source IDs and URLs are unaffected).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

scrapper/src/scrapers/http.ts

@@ -45,3 +45,12 @@ export function decodeEntities(s: string): string {
 }
 
 export const clean = (s: string) => decodeEntities(s).replace(/\s+/g, " ").trim();
+
+/** ASCII URL/ID slug: "Inženir (m/ž)" -> "inzenir-m-z". */
+export const slugify = (s: string) =>
+  s
+    .normalize("NFD")
+    .replace(/[̀-ͯ]/g, "")
+    .replace(/[^A-Za-z0-9]+/g, "-")
+    .replace(/^-|-$/g, "")
+    .toLowerCase();