Adds Azure OpenAI support (#769)

## Summary

This PR introduces support for Azure OpenAI as a provider within the
Codex CLI. Users can now configure the tool to leverage their Azure
OpenAI deployments by specifying `"azure"` as the provider in
`config.json` and setting the corresponding `AZURE_OPENAI_API_KEY` and
`AZURE_OPENAI_API_VERSION` environment variables. This functionality is
added alongside the existing provider options (OpenAI, OpenRouter,
etc.).

Related to #92

**Note:** This PR is currently in **Draft** status because tests on the
`main` branch are failing. It will be marked as ready for review once
the `main` branch is stable and tests are passing.

---

## What’s Changed

-   **Configuration (`config.ts`, `providers.ts`, `README.md`):**
- Added `"azure"` to the supported `providers` list in `providers.ts`,
specifying its name, default base URL structure, and environment
variable key (`AZURE_OPENAI_API_KEY`).
- Defined the `AZURE_OPENAI_API_VERSION` environment variable in
`config.ts` with a default value (`2025-03-01-preview`).
    -   Updated `README.md` to:
        -   Include "azure" in the list of providers.
- Add a configuration section for Azure OpenAI, detailing the required
environment variables (`AZURE_OPENAI_API_KEY`,
`AZURE_OPENAI_API_VERSION`) with examples.
- **Client Instantiation (`terminal-chat.tsx`, `singlepass-cli-app.tsx`,
`agent-loop.ts`, `compact-summary.ts`, `model-utils.ts`):**
- Modified various components and utility functions where the OpenAI
client is initialized.
- Added conditional logic to check if the configured `provider` is
`"azure"`.
- If the provider is Azure, the `AzureOpenAI` client from the `openai`
package is instantiated, using the configured `baseURL`, `apiKey` (from
`AZURE_OPENAI_API_KEY`), and `apiVersion` (from
`AZURE_OPENAI_API_VERSION`).
- Otherwise, the standard `OpenAI` client is instantiated as before.
-   **Dependencies:**
- Relies on the `openai` package's built-in support for `AzureOpenAI`.
No *new* external dependencies were added specifically for this Azure
implementation beyond the `openai` package itself.

---

## How to Test

*This has been tested locally and confirmed working with Azure OpenAI.*

1.  **Configure `config.json`:**
Ensure your `~/.codex/config.json` (or project-specific config) includes
Azure and sets it as the active provider:
    ```json
    {
      "providers": {
        // ... other providers
        "azure": {
          "name": "AzureOpenAI",
"baseURL": "https://YOUR_RESOURCE_NAME.openai.azure.com", // Replace
with your Azure endpoint
          "envKey": "AZURE_OPENAI_API_KEY"
        }
      },
      "provider": "azure", // Set Azure as the active provider
      "model": "o4-mini" // Use your Azure deployment name here
      // ... other config settings
    }
    ```
2.  **Set up Environment Variables:**
    ```bash
    # Set the API Key for your Azure OpenAI resource
    export AZURE_OPENAI_API_KEY="your-azure-api-key-here"

# Set the API Version (Optional - defaults to `2025-03-01-preview` if
not set)
# Ensure this version is supported by your Azure deployment and endpoint
    export AZURE_OPENAI_API_VERSION="2025-03-01-preview"
    ```
3.  **Get the Codex CLI by building from this PR branch:**
Clone your fork, checkout this branch (`feat/azure-openai`), navigate to
`codex-cli`, and build:
    ```bash
    # cd /path/to/your/fork/codex
    git checkout feat/azure-openai # Or your branch name
    cd codex-cli
    corepack enable
    pnpm install
    pnpm build
    ```
4.  **Invoke Codex:**
Run the locally built CLI using `node` from the `codex-cli` directory:
    ```bash
    node ./dist/cli.js "Explain the purpose of this PR"
    ```
*(Alternatively, if you ran `pnpm link` after building, you can use
`codex "Explain the purpose of this PR"` from anywhere)*.
5. **Verify:** Confirm that the command executes successfully and
interacts with your configured Azure OpenAI deployment.

---

## Tests

- [x] Tested locally against an Azure OpenAI deployment using API Key
authentication. Basic commands and interactions confirmed working.

---

## Checklist

- [x] Added Azure provider details to configuration files
(`providers.ts`, `config.ts`).
- [x] Implemented conditional `AzureOpenAI` client initialization based
on provider setting.
-   [x] Ensured `apiVersion` is passed correctly to the Azure client.
-   [x] Updated `README.md` with Azure OpenAI setup instructions.
- [x] Manually tested core functionality against a live Azure OpenAI
endpoint.
- [x] Add/update automated tests for the Azure code path (pending `main`
stability).

cc @theabhinavdas @nikodem-wrona @fouad-openai @tibo-openai (adjust as
needed)

---

I have read the CLA Document and I hereby sign the CLA

codex-cli/src/components/singlepass-cli-app.tsx

@@ -5,13 +5,7 @@ import type { FileOperation } from "../utils/singlepass/file_ops";
 
 import Spinner from "./vendor/ink-spinner"; // Third‑party / vendor components
 import TextInput from "./vendor/ink-text-input";
-import {
-  OPENAI_TIMEOUT_MS,
-  OPENAI_ORGANIZATION,
-  OPENAI_PROJECT,
-  getBaseUrl,
-  getApiKey,
-} from "../utils/config";
+import { createOpenAIClient } from "../utils/openai-client";
 import {
   generateDiffSummary,
   generateEditSummary,
@@ -26,7 +20,6 @@ import { EditedFilesSchema } from "../utils/singlepass/file_ops";
 import * as fsSync from "fs";
 import * as fsPromises from "fs/promises";
 import { Box, Text, useApp, useInput } from "ink";
-import OpenAI from "openai";
 import { zodResponseFormat } from "openai/helpers/zod";
 import path from "path";
 import React, { useEffect, useState, useRef } from "react";
@@ -399,20 +392,7 @@ export function SinglePassApp({
         files,
       });
 
-      const headers: Record<string, string> = {};
-      if (OPENAI_ORGANIZATION) {
-        headers["OpenAI-Organization"] = OPENAI_ORGANIZATION;
-      }
-      if (OPENAI_PROJECT) {
-        headers["OpenAI-Project"] = OPENAI_PROJECT;
-      }
-
-      const openai = new OpenAI({
-        apiKey: getApiKey(config.provider),
-        baseURL: getBaseUrl(config.provider),
-        timeout: OPENAI_TIMEOUT_MS,
-        defaultHeaders: headers,
-      });
+      const openai = createOpenAIClient(config);
       const chatResp = await openai.beta.chat.completions.parse({
         model: config.model,
         ...(config.flexMode ? { service_tier: "flex" } : {}),