docs: add Codex CLI MCP server setup to build-with-ai guide (#13202)

Co-authored-by: Sarah Rainsberger <[email protected]>

Author: Yusaku01

src/content/docs/en/guides/build-with-ai.mdx

@@ -111,6 +111,20 @@ You can configure it to use the Astro Docs MCP server for documentation access b
 
 [More info on using MCP servers with the Claude Code GitHub Action](https://github.com/anthropics/claude-code-action?tab=readme-ov-file#using-custom-mcp-configuration)
 
+#### Codex CLI
+
+Codex CLI is a command-line AI coding tool that can use the Astro Docs MCP server to access documentation while generating Astro code.
+
+You can configure MCP servers at the global level in the `~/.codex/config.toml` file, or in a `.codex/config.toml` file in a project root.
+
+```toml title="~/.codex/config.toml"
+[mcp_servers.astro-docs]
+command = "npx"
+args = ["-y", "mcp-remote", "https://mcp.docs.astro.build/mcp"]
+```
+
+[More info on using MCP servers with Codex CLI](https://developers.openai.com/codex/mcp)
+
 #### Cursor
 
 [Cursor](https://cursor.com) is an AI code editor. Adding the Astro Docs MCP server allows Cursor to access the latest Astro documentation while performing development tasks.