feat: Add OpenAI API type configuration and update provider settings

docs/configuration.md

@@ -167,6 +167,26 @@ ANTHROPIC_API_KEY="$(bw get password api/anthropic)" nanobot agent
 | `github_copilot` | LLM (GitHub Copilot, OAuth) | `nanobot provider login github-copilot` |
 | `qianfan` | LLM (Baidu Qianfan) | [cloud.baidu.com](https://cloud.baidu.com/doc/qianfan/s/Hmh4suq26) |
 
+<details>
+<summary><b>OpenAI</b></summary>
+
+By default, OpenAI uses `apiType: "auto"`: nanobot calls Chat Completions normally and routes GPT-5/o-series or explicit `reasoningEffort` requests through the Responses API when useful. You can force a specific API surface:
+
+```json
+{
+  "providers": {
+    "openai": {
+      "apiKey": "${OPENAI_API_KEY}",
+      "apiType": "chat_completions"
+    }
+  }
+}
+```
+
+Valid `apiType` values are exactly `auto`, `chat_completions`, and `responses`.
+
+</details>
+
 <details>
 <summary><b>Skywork / APIFree</b></summary>