feat(ai): add Kimi Code subscription OAuth login (#6935)

Add a device authorization grant flow (RFC 8628) for the kimi-coding
provider, mirroring the official Kimi Code CLI: device authorization and
token polling against https://auth.kimi.com, refresh-token rotation with
retry/backoff, and Bearer auth via toAuth headers. The provider now
offers 'Sign in with Kimi Code' alongside the existing KIMI_API_KEY
auth. Host is overridable via KIMI_CODE_OAUTH_HOST / KIMI_OAUTH_HOST.

Co-authored-by: Mario Zechner <badlogicgames@gmail.com>

packages/ai/src/providers/kimi-coding.ts

@@ -1,5 +1,6 @@
 import { anthropicMessagesApi } from "../api/anthropic-messages.lazy.ts";
-import { envApiKeyAuth } from "../auth/helpers.ts";
+import { envApiKeyAuth, lazyOAuth } from "../auth/helpers.ts";
+import { loadKimiCodingOAuth } from "../auth/oauth/load.ts";
 import { createProvider, type Provider } from "../models.ts";
 import { KIMI_CODING_MODELS } from "./kimi-coding.models.ts";
 
@@ -8,7 +9,14 @@ export function kimiCodingProvider(): Provider<"anthropic-messages"> {
 		id: "kimi-coding",
 		name: "Kimi For Coding",
 		baseUrl: "https://api.kimi.com/coding",
-		auth: { apiKey: envApiKeyAuth("Kimi API key", ["KIMI_API_KEY"]) },
+		auth: {
+			apiKey: envApiKeyAuth("Kimi API key", ["KIMI_API_KEY"]),
+			oauth: lazyOAuth({
+				name: "Kimi Code (subscription)",
+				loginLabel: "Sign in with Kimi Code",
+				load: loadKimiCodingOAuth,
+			}),
+		},
 		models: Object.values(KIMI_CODING_MODELS),
 		api: anthropicMessagesApi(),
 	});