Replace manual token input with Hugging Face OAuth login

Modularize chat completion and add loading and typing animation

Add ChatSettings component with slider-based parameter control

Support user-provided HF token instead of env variable

Connect user input to HF chatCompletion and display assistant response

Setup Hugging Face InferenceClient using REACT_APP_HF_TOKEN

Extract MessageInput, MessageBubble and MessagePair components

Create chat UI