feat(ai): add xAI device OAuth and route grok-4.5 through Responses (#6651)

* feat(ai): add xAI device OAuth and route grok-4.5 through Responses

Add xAI device-code OAuth alongside XAI_API_KEY. Route only grok-4.5
through Responses with low/medium/high reasoning; other xAI models stay
on Completions.

* fix(ai): tolerate xAI device-code interval 0 and correct token poll error label

---------

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

packages/ai/src/providers/xai.models.ts

@@ -97,11 +97,12 @@ export const XAI_MODELS = {
 	"grok-4.5": {
 		id: "grok-4.5",
 		name: "Grok 4.5",
-		api: "openai-completions",
+		api: "openai-responses",
 		provider: "xai",
 		baseUrl: "https://api.x.ai/v1",
-		compat: {"supportsStore":false,"supportsDeveloperRole":false,"supportsReasoningEffort":false},
+		compat: {"supportsLongCacheRetention":false},
 		reasoning: true,
+		thinkingLevelMap: {"off":null,"minimal":null},
 		input: ["text", "image"],
 		cost: {
 			input: 2,
@@ -111,7 +112,7 @@ export const XAI_MODELS = {
 		},
 		contextWindow: 500000,
 		maxTokens: 500000,
-	} satisfies Model<"openai-completions">,
+	} satisfies Model<"openai-responses">,
 	"grok-build-0.1": {
 		id: "grok-build-0.1",
 		name: "Grok Build 0.1",