Add per-choice mean RT to dashboard stats table

Render `_s*` model plots at expected variability + per-sample NDT

Fix broken app: migrate to Simulator class + NumPy 2.x compat

change banner text and adjust v and t default settings

add disclaimer

transpose table to allow arrow serialization

change title

bunch of visual improvements and first round of exposing styling options to users

initial test

Duplicate from streamlit/streamlit-template-space