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>

install.sh

@@ -69,7 +69,7 @@ if [[ ! -f "$CREDS_FILE" ]]; then
     "password": "secret"
   },
   "vin":        "",
-  "domains":    ["charging", "measurements", "readiness"],
+  "domains":    ["charging", "electric_drive", "connectivity"],
   "interval_s": 300,
   "host":       "0.0.0.0",
   "port":       9999,
@@ -93,7 +93,7 @@ mkdir -p "$SYSTEMD_DIR"
 
 cat > "$SERVICE_FILE" <<EOF
 [Unit]
-Description=WeConnect vehicle data collector
+Description=CarConnectivity vehicle data collector
 After=network-online.target
 Wants=network-online.target