refactor(ui): simplify pipeline progress display with st.progress bar

feat: enhance UI with evidence links, journey guards, and gap phrasing

feat: wire real API pipeline with demo mode and Gemini truncation fix

style: apply ruff format to entire codebase

fix: replace asyncio.run() with thread-safe sync bridge for Streamlit

feat: connect UI pages to Parlant

fix: move entrypoint to project root, fix P0 ModuleNotFoundError

feat: implement 5 Streamlit pages, app.py entrypoint, and mock data