Fix conversation memory duplication bug

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Description

Fixes conversation memory duplication where user messages appeared twice in API requests sent to the LLM.

The bug occurred in both stream() and streamEvents() methods - the current user message was being added to conversationHistory
BEFORE sending the request to the LLM, which meant it appeared in both the chat_history array and the input parameter.

This fix moves the addToHistory() call to AFTER the LLM completes processing, ensuring conversation history only contains previous
messages during LLM processing.

Type of change

• Bug fix (non-breaking change which fixes an issue)

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have added tests that prove my fix is effective or that my feature works
• The title of my pull request follows the conventional commits standard
• Changes have been documented in the README/documentation (if applicable)

Note: I left "tests" and "documentation" unchecked since:

• You tested it manually but didn't add automated tests
• This is a bug fix that doesn't need documentation updates