🔧 chore(chat.py): add missing build step for root node in graph

📝 docs(chat.py): explain the need for building the root node before the rest of the graph
The root node in the graph was not being built before the rest of the graph, which caused issues when certain nodes required parameters that were not connected to them. By adding the missing build step for the root node, we ensure that all necessary connections and parameters are properly set up before building the rest of the graph. This improves the overall functionality and reliability of the chat module.