Use the stable OpenAI app reference

[thebiglabasky]

Summary

• replace the callback-specific development app reference with the OpenAI submission app that uses the stable CIMD identity
• rename the manifest alias from the generated development ID to checkly

Rationale

OpenAI introduced the stable ChatGPT CIMD client ID and redirect for authorization servers that support issuer identification. Checkly supports that flow, and the OpenAI plugin submission already authenticates through:

• client ID: https://chatgpt.com/oauth/client.json
• redirect URI: https://chatgpt.com/connector_platform_oauth_redirect

Keeping the repository-installed plugin on a separate callback-specific app creates two ChatGPT OAuth clients in Auth0. That makes scope and grant changes easy to apply to one path while missing the other. Pointing the plugin at the submission app gives us one intended ChatGPT OAuth posture alongside the existing single Claude posture.

Official guidance:

• https://developers.openai.com/plugins/build/auth#client-registration
• https://developers.openai.com/plugins/changelog

Merge gate

This is intentionally a draft. Before merging:

• Stefan confirms asdk_app_6a7f1be5a9e48191b23a7b6ae73cf976 is the canonical OpenAI submission app
• confirm that the app is available to users installing the plugin from the GitHub marketplace, or wait until the OpenAI submission is approved and published
• perform a fresh Codex/ChatGPT install and verify authentication uses https://chatgpt.com/oauth/client.json
• verify the resulting token can receive every scope advertised by the Checkly MCP server

The callback-specific Auth0 client is still active and must not be deleted as part of this PR. Retire it separately only after existing installations have migrated and its refresh-token activity has stopped.

Validation

• npm test
• npm run lint
• npm run format:check
• npm run typecheck
• manifest JSON assertion and git diff --check