plotly/dash ? reverse-engineered prompt

Build me a simple Dash app in Python for exploring data with interactive charts and controls.

I want a clean web dashboard where I can upload or load a dataset, pick a few filters from dropdowns and sliders, and see the graphs update right away. It should include at least one main Plotly chart, a summary section with a few key numbers, and a layout that looks polished on desktop and still works nicely in a browser. Please keep it all in Python, no JavaScript needed.

Make it easy to swap in different datasets later, and structure it so I can add more charts or controls without rewriting everything. If there are any current best practices or helpful docs for Dash, look them up online and follow them. Add a small example dataset or demo view so I can run it and see how it works right away.