feat(xai): prefilled OAuth device link, SuperGrok login label, trimmed model list (#6734)

- Use verification_uri_complete from the xAI device-code response so the
  login link opens with the user code prefilled (https-validated)
- Add OAuthAuth.loginLabel and show "Sign in with SuperGrok or X Premium"
  in the xAI auth-type selector (threaded through lazyOAuth)
- Remove grok-3, grok-3-fast, grok-4.20 variants and grok-code-fast-1
  from the built-in xAI catalog and default to grok-4.5

Co-authored-by: Jaaneek <Jaaneek@users.noreply.github.com>

packages/ai/test/stream.test.ts

@@ -543,7 +543,7 @@ describe("Generate E2E Tests", () => {
 	});
 
 	describe.skipIf(!process.env.XAI_API_KEY)("xAI Provider (grok-code-fast-1 via OpenAI Completions)", () => {
-		const llm = getModel("xai", "grok-code-fast-1");
+		const llm = getModel("xai", "grok-4.3");
 
 		it("should complete basic text generation", { retry: 3 }, async () => {
 			await basicTextGeneration(llm);