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.

open-sse/providers/registry/index.js

@@ -121,6 +121,7 @@ import p118 from "./selfhosted-tts.js";
 import p119 from "./selfhosted-embedding.js";
 import p120 from "./fish-audio.js";
 import p121 from "./alitp-intl.js";
+import p122 from "./xquik.js";
 
 export default [
   p0,
@@ -243,4 +244,5 @@ export default [
   p119,
   p120,
   p121,
+  p122,
 ];