Selects Chainlit as the chat UI library (AI-native, Python, handles WebSocket/streaming/session out of the box). Establishes Python as the project language. Documents accessibility gap mitigations (ARIA live regions, focus management, reduced-motion, contrast overrides). Defines project layout and Chainlit configuration. https://claude.ai/code/session_01SUWzMzFvSfWiHXA2p6rPg9