feat: redesign bench calibration (factor/offset), add Ttank/P2 displays, fix sensor calibration

- Replace P1-P6 rational transfer function with factor/offset model for bench params
- Add explicit rx/tx direction flags in bench XML configuration
- Add T.Tank (BenchTemp) and P2 (AnalogSensor2) to temperature/pressure display
- Apply SensorConfiguration calibration to pressure channels, fix empty sensors.xml fallback
- Add live value labels to flowmeter charts
- Hide pump live values and PSG encoder standalone label
- Add K-Line connection state model, improve KWP service and status displays
- Restructure .claude/skills into subdirectory format

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

ViewModels/SingleFlowChartViewModel.cs

@@ -23,6 +23,9 @@ namespace HC_APTBS.ViewModels
         /// <summary>Chart title label.</summary>
         [ObservableProperty] private string _title = string.Empty;
 
+        /// <summary>Most recent sample value, displayed as a numeric label alongside the chart.</summary>
+        [ObservableProperty] private double _currentValue;
+
         /// <summary>Series array bound to the CartesianChart.</summary>
         public ISeries[] Series { get; }
 
@@ -88,6 +91,7 @@ namespace HC_APTBS.ViewModels
         public void AddValue(double value)
         {
             _values.Add(value);
+            CurrentValue = value;
             if (_values.Count > _maxSamples)
                 _values.RemoveAt(0);
         }