feat(grok-cli): add Grok CLI / Grok Build provider with OAuth device-code flow (#2502)

New OAuth provider routing through cli-chat-proxy.grok.com (OpenAI Responses
API), distinct from xai (api.x.ai) and grok-web (cookie SSO):

- Registry + GrokCliExecutor: Chat Completions -> Responses transform, CLI
  fingerprint headers, virtual effort models grok-4.5-{low,medium,high}
- OAuth device-code flow (auth.x.ai) with no-PKCE, shared xAI token refresh
- store=false multi-turn continuity via reasoning encrypted_content
- Quota tracker: on-demand window + prepaid balance on dashboard
- Connection test: 402 spending-limit = soft success (auth OK, out of credits)
- Alias/oauth/provider baselines + unit tests

tests/unit/usage-dispatch.test.js

@@ -15,7 +15,7 @@ const load = () => import("../../open-sse/services/usage.js");
 const SUPPORTED = [
   "github", "gemini-cli", "antigravity", "claude", "codex", "kiro",
   "qoder", "qwen", "iflow", "ollama", "glm", "glm-cn",
-  "minimax", "minimax-cn", "vercel-ai-gateway",
+  "minimax", "minimax-cn", "vercel-ai-gateway", "grok-cli",
 ];
 
 describe("usage dispatch", () => {