FIX: Use langchain_classic.memory for ConversationBufferWindowMemory (langchain 0.3.27 has memory under langchain_classic, not langchain)

Fix langchain imports: use langchain.memory for ConversationBufferWindowMemory, use langchain_core.tools for BaseTool (langchain 0.3.27 compatibility)

Fix: Resolve all import errors and dependency issues

feat: testing done