feat: v1

[loks0n]

• Move vector store initialization to a dedicated script and save index to disk
• Switch from basic Q&A chain to a streaming chat chain that maintains conversation history
• Update dependencies including langchain, hnswlib-node, and other core packages
• Remove direct OpenAI chat implementation in favor of langchain chat model
• Add basic health check endpoint
• Add API endpoint for chat conversations (/v1/chat)