feat: Add confirmation question flow and multilingual support to research agent

[kahirokunn]

Overview

This PR introduces two major features that significantly enhance the research agent's capabilities:

1. Confirmation Question Flow: An interactive confirmation step to clarify user intent
2. Multilingual Support: Automatic language detection and response generation in the user's language

Changes

🎯 Confirmation Question Flow

The agent can now ask clarifying questions before starting research to ensure better understanding of user requirements.

Key changes:

• Add confirmation_completed and skip_confirmation fields to OverallState
• Create confirmation_question node to generate clarifying questions
• Implement conditional routing based on user intent and conversation state
• Add ConfirmationQuestion schema for structured output
• Update graph flow to include confirmation step before research

Benefits:

• Generates more accurate and relevant research results
• Resolves ambiguity in user requests
• Prevents unnecessary research execution

🌐 Multilingual Support

All prompts and responses are now automatically generated in the user's language.

Key changes:

• Add language instructions to all prompts to respond in user's language
• Update the following instructions:
  • query_writer_instructions
  • reflection_instructions
  • answer_instructions
  • confirmation_question_instructions
• Enable automatic language detection and response generation in the same language

Supported languages:

• Japanese, English, Chinese, Korean
• Any other language supported by the LLM

Testing

• Verify confirmation question flow works correctly
• Confirm Japanese input receives Japanese response
• Confirm English input receives English response
• Verify skip confirmation option works properly

Related Issues

N/A

Notes

These features enable us to provide a better user experience for a more diverse user base.

[kahirokunn]

@philschmid Would you mind reviewing it when you have time?
Thank you.