- Replace 8-point scatter chart with proper 60-point line chart
- Blue gradient fill (rgba 35%→2%), tension 0.4 smooth curve
- No legend (obvious), no X axis grid, soft Y axis gridlines
- Y axis auto-scales: max(60, sessionMax*1.2) rounded to 10s
- Ticks: '0 km/h' labels on Y, time strings on X (max 6)
- chart.update('none') for live updates (no animation stutter)
- Speed history card header now shows current speed + session max
even when the graph is collapsed
- Footer bar inside expanded graph: session avg, point count, last reading time
- makeGradient() refreshed on every update in case canvas was resized
- obd_rpm now appends ' rpm' to the displayed value
Co-authored-by: Copilot <[email protected]>
