Zaraa7/phase3-todo-api

Fix: Add error handling for JSON parsing and stream fallback

Fix: Use correct model with fallback for tool call errors

Fix: Switch to stable model, skip history for tool calls, add error handling

Add error logging to debug 500 errors

Fix: UUID type and assistant message serialization for chat

Update app/routers/chat.py

Update app/routers/chat.py

Update app/routers/chat.py

Phase III: AI-Native Todo Chatbot Backend