feat(search): add Xquik as an X search provider

Xquik needs a GET request with x-api-key auth and a tweets envelope
normalizer, neither of which the generic search fallback provides. Adds a
dedicated request builder and normalizer, cursor pagination passthrough,
result-based credit usage reporting, and a validateUrl probe so key
validation hits the no-charge credits endpoint.

src/app/api/providers/validate/route.js

@@ -20,7 +20,7 @@ async function probeWebProvider(provider, apiKey) {
   if (!cfg) return null;
   if (cfg.authType === "none") return true; // no-auth (e.g. searxng)
 
-  let url = cfg.baseUrl;
+  let url = cfg.validateUrl || cfg.baseUrl;
   const headers = { "Content-Type": "application/json" };
   let body;
 

src/shared/constants/skills.js

@@ -56,7 +56,7 @@ export const SKILLS = [
   {
     id: "9router-web-search",
     name: "Web Search",
-    description: "Tavily / Exa / Brave / Serper / SearXNG / Google PSE / You.com.",
+    description: "Web and X search via Tavily / Exa / Brave / Serper / SearXNG / Google PSE / You.com / Xquik.",
     endpoint: "/v1/search",
     icon: "search",
   },