Replaces row/col grid with a resizable splitter at 66/34 ratio,
matching the original Streamlit st.columns([2, 1]) layout. Removes
extra card wrapper from sequences to maximize content width.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Add page/sidebar background contrast, wrap action button rows,
ensure dark text in inputs, and improve timeline card highlight colors.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>