Turns an uploaded dataset (.xlsx, .csv, .json, or PDF tables) into a self-contained, scroll-driven HTML data story with animated Plotly charts, counting stat cards, and narrative chapters. Use when the user asks for a data story, scrollytelling report, or an interactive narrative write-up of a dataset. If the user asks for a demo or example with no dataset of their own, build the story from the bundled sample workbook at assets/Basketball_Demo_Data.xlsx.
