feat: add xAI Grok provider support

src/commands/onboard-auth.ts

@@ -24,6 +24,8 @@ export {
   applyXiaomiConfig,
   applyXiaomiProviderConfig,
   applyZaiConfig,
+  applyXaiConfig,
+  applyXaiProviderConfig,
 } from "./onboard-auth.config-core.js";
 export {
   applyMinimaxApiConfig,
@@ -54,10 +56,12 @@ export {
   setVercelAiGatewayApiKey,
   setXiaomiApiKey,
   setZaiApiKey,
+  setXaiApiKey,
   writeOAuthCredentials,
   VERCEL_AI_GATEWAY_DEFAULT_MODEL_REF,
   XIAOMI_DEFAULT_MODEL_REF,
   ZAI_DEFAULT_MODEL_REF,
+  XAI_DEFAULT_MODEL_REF,
 } from "./onboard-auth.credentials.js";
 export {
   buildMinimaxApiModelDefinition,