docs: add useComplitionApi option for OpenAI-compatible providers in agent modes

Author: NoOne7135

adminforth/documentation/docs/tutorial/05-Adapters/05-ai-completion-adapters.md

@@ -134,12 +134,25 @@ new CompletionAdapterOpenAIResponses({
   openAiApiKey: process.env.OVH_AI_ENDPOINTS_ACCESS_TOKEN as string,
   baseUrl: 'https://oai.endpoints.kepler.ai.cloud.ovh.net/v1',
   model: 'gpt-oss-20b',
+  useComplitionApi: true,
   extraRequestBodyParameters: {
     store: false,
   },
 }),
 ```
 
+For LangChain agent mode, `useComplitionApi` controls which provider API is used:
+
+- `false` uses the OpenAI `responses` API
+- `true` uses the Chat Completions API
+
+If `useComplitionApi` is omitted, the adapter keeps the current default behavior:
+
+- official OpenAI uses the `responses` API
+- custom `baseUrl` providers use the Chat Completions API
+
+OVH AI Endpoints still does not fully support the `responses` API, so `useComplitionApi: false` may work unstably there.
+
 
 
 ## Google Gemini Completion Adapter
@@ -179,4 +192,4 @@ new CompletionAdapterGoogleGemini({
     responseMimeType: 'application/json',
   },
 }),
-```
+```

adminforth/documentation/docs/tutorial/08-Plugins/26-agent.md

@@ -278,6 +278,19 @@ plugins: [
 ]
 ```
 
+When using OpenAI-compatible providers for agent modes, you can force Chat Completions API mode with `useComplitionApi: true`:
+
+```ts
+completionAdapter: new CompletionAdapterOpenAIResponses({
+  openAiApiKey: process.env.OVH_AI_ENDPOINTS_ACCESS_TOKEN as string,
+  baseUrl: 'https://oai.endpoints.kepler.ai.cloud.ovh.net/v1',
+  model: 'gpt-oss-20b',
+  useComplitionApi: true,
+})
+```
+
+OVH AI Endpoints still does not fully support the OpenAI `responses` API, so `useComplitionApi: false` may work unstably there.
+
 Each item in `modes` defines a user-selectable preset in the chat UI. The selected mode is sent to the backend and the plugin uses that mode's `completionAdapter` for the response.
 
 The plugin adds a chat surface to the admin UI, keeps session history per admin user, and shows a mode picker when `modes` are configured.