feat: onroad health overlay + 2x tire path in nightrider

System health overlay:
- Lower-right 5-metric panel: LAG (controlsState.cumLagMs), DROP
  (modelV2.frameDropPerc), TEMP (deviceState.maxTempC), CPU (max core of
  deviceState.cpuUsagePercent), MEM (deviceState.memoryUsagePercent)
- Color-coded white→yellow→red by severity (LAG: 50/200ms, DROP: 5/15%,
  TEMP: 75/88°C, CPU: 75/90%, MEM: 70/85%)
- Toggle in ClearPilot → Debug → "System Health Overlay"
- New param ClearpilotShowHealthMetrics, PERSISTENT (disk, survives
  reboots), default false — re-polled every ~2s so toggle takes effect
  without process restart
- InterFont(90, Bold) to match speed limit numeric styling, 30px margin,
  40px between rows, black rounded background

Nightrider center lane path (the "tire track" polygon from
scene.track_vertices) is now drawn at 2x the width of other lines —
highlights the planned path distinctly against the otherwise stark
outline-only rendering.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

common/params.cc

@@ -292,6 +292,7 @@ std::unordered_map<std::string, uint32_t> keys = {
     {"CEStopLights", PERSISTENT},
     {"CEStopLightsLead", PERSISTENT},
     {"Compass", PERSISTENT},
+    {"ClearpilotShowHealthMetrics", PERSISTENT},
     {"ConditionalExperimental", PERSISTENT},
     {"CrosstrekTorque", PERSISTENT},
     {"CurrentHolidayTheme", PERSISTENT},