AI Comprehensive Research on User's Query (reproduction of gemini-fullstack-langgraph-quickstart)

## reflection()

Identifies knowledge gaps and generates potential follow-up queries. 
Analyzes the current summary to identify areas for further research 
and generates potential follow-up queries. 

#### Why use `HTTP Reuquest` node to send raw gemini chat request insteam of using builtin node ?
The output structured feature of builtin node can only attach schema text with prompt, it will not configure the `Structured output schema` of gemini api.
When context becomes large, it will occasionally get wrong results.