feat(searxng): configure endpoint via SEARXNG_URL env (#2499)

Add SEARXNG_URL runtime override for the built-in SearXNG web-search
provider, defaulting to http://localhost:8888/search. Enables Docker
and remote SearXNG deployments without changing existing behavior.

Co-authored-by: Cursor <cursoragent@cursor.com>

open-sse/providers/registry/searxng.js

@@ -1,3 +1,5 @@
+import { SEARXNG_URL } from "../../config/runtimeConfig.js";
+
 export default {
   id: "searxng",
   alias: "searxng",
@@ -15,7 +17,7 @@ export default {
   ],
   noAuth: true,
   searchConfig: {
-    baseUrl: "http://localhost:8888/search",
+    baseUrl: SEARXNG_URL,
     method: "GET",
     authType: "none",
     authHeader: "none",