docs: add codex to zen

packages/web/src/content/docs/zen.mdx

@@ -64,7 +64,8 @@ You can also access our models through the following API endpoints.
 
 | Model            | Mode ID          | Endpoint                                      | AI SDK Package              |
 | ---------------- | ---------------- | --------------------------------------------- | --------------------------- |
-| GPT-5            | gpt-5            | `https://opencode.ai/zen/v1/responses`        | `@ai-sdk/openai`            |
+| GPT 5            | gpt-5            | `https://opencode.ai/zen/v1/responses`        | `@ai-sdk/openai`            |
+| GPT 5 Codex           | gpt-5-codex            | `https://opencode.ai/zen/v1/responses`        | `@ai-sdk/openai`            |
 | Claude Sonnet 4  | claude-sonnet-4  | `https://opencode.ai/zen/v1/messages`         | `@ai-sdk/anthropic`         |
 | Claude Haiku 3.5 | claude-3-5-haiku | `https://opencode.ai/zen/v1/messages`         | `@ai-sdk/anthropic`         |
 | Claude Opus 4.1  | claude-opus-4-1  | `https://opencode.ai/zen/v1/messages`         | `@ai-sdk/anthropic`         |
@@ -88,6 +89,7 @@ We support a pay-as-you-go model. Below are the prices **per 1M tokens**.
 | Claude Haiku 3.5                | $0.80  | $4.00  | $0.08       | $1.00        |
 | Claude Opus 4.1                 | $15.00 | $75.00 | $1.50       | $18.75       |
 | GPT 5                           | $1.25  | $10.00 | $0.125      | -            |
+| GPT 5 Codex                     | $1.25  | $10.00 | $0.125      | -            |
 | Kimi K2                         | $0.60  | $2.50  | -           | -            |
 
 :::note