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/bun-oauth.ts

@@ -1,5 +1,6 @@
 import { anthropicOAuth } from "./auth/oauth/anthropic.ts";
 import { githubCopilotOAuth } from "./auth/oauth/github-copilot.ts";
+import { kimiCodingOAuth } from "./auth/oauth/kimi-coding.ts";
 import { registerBundledOAuthFlowLoaders } from "./auth/oauth/load.ts";
 import { openaiCodexOAuth } from "./auth/oauth/openai-codex.ts";
 import { createRadiusOAuth } from "./auth/oauth/radius.ts";
@@ -11,6 +12,7 @@ export function registerBunOAuthFlows(): void {
 		anthropic: () => anthropicOAuth,
 		openaiCodex: () => openaiCodexOAuth,
 		githubCopilot: () => githubCopilotOAuth,
+		kimiCoding: () => kimiCodingOAuth,
 		xai: () => xaiOAuth,
 		radius: createRadiusOAuth,
 	});