Add basic chatbot frontend

Add a sub api called `front` to access the admin and the chatbot.

the chatbot is a basic chat ui with auto response from the intellinode chat providers:
- Openai.

In the next step we will add the following providers:
- llama.
- Google Palm.

Start by locating the proposed `front` sub-API and the existing admin entry point. Define the basic chat UI and OpenAI auto-response behavior, then verify that the frontend can access both admin and chatbot routes. Llama and Google Palm support is explicitly deferred to a later step.

Do mô hình lập chỉ mục viết ra từ nội dung của issue.