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/StatusDisplayViewModel.cs

@@ -40,6 +40,9 @@ namespace HC_APTBS.ViewModels
             get => _isActive;
             set => SetProperty(ref _isActive, value);
         }
+
+        /// <summary>Zero-based bit position (0–15) shown as a label beneath the indicator.</summary>
+        public int Index { get; init; }
     }
 
     /// <summary>
@@ -73,7 +76,7 @@ namespace HC_APTBS.ViewModels
         public StatusDisplayViewModel()
         {
             for (int i = 0; i < 16; i++)
-                Bits.Add(new BitIndicatorViewModel { Color = "#26C200", Description = $"Bit {i}" });
+                Bits.Add(new BitIndicatorViewModel { Color = "#26C200", Description = $"Bit {i}", Index = i });
         }
 
         // ── Public API ────────────────────────────────────────────────────────────