[DCV-3774] Document OpenAI Codex integration

docs/how-tos/vs-code/external-ai-tools/_category_.yaml

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+label: External AI Tools
+position: 45
+link:
+  type: generated-index
+  title: External AI Tools
+  description: Configure and use external AI coding assistants in Datacoves.

docs/how-tos/vs-code/external-ai-tools/openai-codex.md

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+---
+title: OpenAI Codex
+sidebar_position: 1
+---
+
+# OpenAI Codex
+
+[OpenAI Codex](https://openai.com/codex/) is an AI coding assistant available as both a CLI tool and a VS Code extension in Datacoves.
+
+## Prerequisites
+
+- A [ChatGPT](https://chatgpt.com) account
+- Codex enabled in your Datacoves environment. Contact [Datacoves support](mailto:support@datacoves.com) to enable it.
+
+## Enable device code login
+
+Before logging in from Datacoves, enable device code login in your ChatGPT account.
+
+**Personal accounts:** go to your [ChatGPT security settings](https://chatgpt.com/security-settings) and enable device code login.
+
+**Workspace / Enterprise accounts:** a workspace admin must enable device code authentication in the [admin permissions](https://chatgpt.com/admin/permissions) page.
+
+For more details, see [OpenAI's authentication docs](https://developers.openai.com/codex/auth).
+
+## Login
+
+1. Open a terminal in your Datacoves VS Code workspace
+
+2. Run:
+
+   ```bash
+   codex login --device-auth
+   ```
+
+3. The CLI will display a URL and a one-time code
+
+4. Open the URL in any browser, enter the code, and sign in with your ChatGPT account
+
+Both the CLI and the VS Code extension are now authenticated.
+
+:::note
+You may need to reload your browser tab after CLI login for the VS Code extension to pick up the credentials.
+:::
+
+## Learn more
+
+- [OpenAI Codex documentation](https://developers.openai.com/codex)
+- [Codex authentication](https://developers.openai.com/codex/auth)
+- [Codex CLI reference](https://developers.openai.com/codex/cli/reference)