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/chat/terminal-chat.tsx

@@ -13,7 +13,7 @@ import { useTerminalSize } from "../../hooks/use-terminal-size.js";
 import { AgentLoop } from "../../utils/agent/agent-loop.js";
 import { ReviewDecision } from "../../utils/agent/review.js";
 import { generateCompactSummary } from "../../utils/compact-summary.js";
-import { getBaseUrl, getApiKey, saveConfig } from "../../utils/config.js";
+import { saveConfig } from "../../utils/config.js";
 import { extractAppliedPatches as _extractAppliedPatches } from "../../utils/extract-applied-patches.js";
 import { getGitDiff } from "../../utils/get-diff.js";
 import { createInputItem } from "../../utils/input-utils.js";
@@ -23,6 +23,7 @@ import {
   calculateContextPercentRemaining,
   uniqueById,
 } from "../../utils/model-utils.js";
+import { createOpenAIClient } from "../../utils/openai-client.js";
 import { CLI_VERSION } from "../../utils/session.js";
 import { shortCwd } from "../../utils/short-path.js";
 import { saveRollout } from "../../utils/storage/save-rollout.js";
@@ -34,7 +35,6 @@ import ModelOverlay from "../model-overlay.js";
 import chalk from "chalk";
 import { Box, Text } from "ink";
 import { spawn } from "node:child_process";
-import OpenAI from "openai";
 import React, { useEffect, useMemo, useRef, useState } from "react";
 import { inspect } from "util";
 
@@ -78,10 +78,7 @@ async function generateCommandExplanation(
 ): Promise<string> {
   try {
     // Create a temporary OpenAI client
-    const oai = new OpenAI({
-      apiKey: getApiKey(config.provider),
-      baseURL: getBaseUrl(config.provider),
-    });
+    const oai = createOpenAIClient(config);
 
     // Format the command for display
     const commandForDisplay = formatCommandForDisplay(command);