Reaction Time Transformations and Visualizations

[samuelbaldwin05]

Backend transformation and frontend KPI card for the Reaction Time standalone test.

Tasks

• Backend: add transformation to detect time from stimulus to first GCT onset from force plate data
• Expose via new endpoint (standalone test, does not use universal metrics pipeline)
• Frontend: KPI card with color zones — 🟢 <200ms / 🟡 200–300ms / 🔴 >300ms
• Add info card describing the metric (elite sprinters <150ms, false start threshold <100ms)
• Submit screenshot