feat(xai): track SuperGrok weekly limit + API usage quota

Fetch OAuth quota from cli-chat-proxy billing, GetGrokCreditsConfig weekly
window, and settings plan label so the dashboard matches grok.com usage.

open-sse/services/usage.js

@@ -11,6 +11,7 @@ export { consumeCodexRateLimitResetCredit, getCodexRateLimitResetCredits };
 import { getKiroUsage } from "./usage/kiro.js";
 import { getMiniMaxUsage } from "./usage/minimax.js";
 import { getCodeBuddyCnUsage } from "./usage/codebuddy-cn.js";
+import { getXaiUsage } from "./usage/xai.js";
 import {
   getQwenUsage,
   getIflowUsage,
@@ -43,6 +44,7 @@ const USAGE_HANDLERS = {
   "minimax-cn": (c) => getMiniMaxUsage(c.apiKey, c.provider, c.proxyOptions),
   "vercel-ai-gateway": (c) => getVercelAiGatewayUsage(c.apiKey, c.proxyOptions),
   "codebuddy-cn": (c) => getCodeBuddyCnUsage(c.accessToken, c.apiKey, c.providerSpecificData, c.proxyOptions),
+  xai: (c) => getXaiUsage(c.accessToken, c.proxyOptions),
 };
 
 export async function getUsageForProvider(connection, proxyOptions = null) {