Update clients, docs, and install for CarConnectivity migration

- gui_client: update _TRACE_LABELS paths to new flat snapshot structure
- README: update library name, pip command, domain list, credentials
  template, output example, and module reference
- install.sh: update credentials template and systemd service description
- client.py: update docstring
- data_model: Kelvin→Celsius conversion for battery temps (CarConnectivity
  returns Kelvin); round range_estimated_full to 1 decimal
- jay_diff: fix merge when old value is not a dict; skip empty-dict
  branches in delete

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

server/data_model.py

@@ -118,13 +118,13 @@ def extract_electric_drive(vehicle) -> dict | None:
     try:
         ed = vehicle.get_electric_drive()
         result["range"] = _phys(ed.range.value, "km")
-        result["range_full"] = _phys(ed.range_estimated_full.value, "km")
+        result["range_full"] = _phys(round(float(ed.range_estimated_full.value), 1), "km")
         try:
             bat = ed.battery
             result["battery"] = {
                 "soc": _phys(ed.level.value, "%"),
-                "temperature_max": _phys(bat.temperature_max.value, "degC"),
-                "temperature_min": _phys(bat.temperature_min.value, "degC"),
+                "temperature_max": _phys(round(float(bat.temperature_max.value) - 273.15, 1), "degC"),
+                "temperature_min": _phys(round(float(bat.temperature_min.value) - 273.15, 1), "degC"),
             }
         except Exception:
             log.debug("electric_drive/battery unavailable", exc_info=True)