feat: UI test mode + per-game port configuration

- Settings: UI test mode toggle generates simulated telemetry data (speed/RPM/gear/laps...)
- Simulated data broadcasts via WebSocket and forwards to downstream devices
- game_ports config: per-game independent port overrides (shown when unified port off)
- Settings UI: game port list with save button, hidden when unified port enabled
- Sidebar: switch game reads game_ports[gameId] fallback to default_port

server/api.py

@@ -72,6 +72,18 @@ async def api_stop_telemetry():
     return {"ok": True, "running": telemetry_listener.is_running}
 
 
+@router.post("/test-mode/start")
+async def api_start_test_mode():
+    telemetry_listener.start_test_mode()
+    return {"ok": True, "testing": True}
+
+
+@router.post("/test-mode/stop")
+async def api_stop_test_mode():
+    telemetry_listener.stop_test_mode()
+    return {"ok": True, "testing": False}
+
+
 @router.get("/telemetry/latest")
 async def api_latest_telemetry():
     latest = telemetry_listener.latest_data