docs: refine dashboard demo

[stianfro]

Summary

• remove the first two recorded frames from the dashboard GIF
• move the dashboard GIF from the Usage section to the project introduction
• keep the animation at 800 by 649 pixels with an 11.33 second playback time

Verification

• inspected the trimmed first frame
• verified the GIF frame count, dimensions, and playback time
• git diff --check