sparkline: unified coloring - vertical gradient from colorAt/thresholds, stroke line, 1px border, consistent 32px height

shell/applets/BatteryApplet.qml

@@ -86,18 +86,16 @@ Column {
         }
     }
 
-    // 24h history sparkline (area chart)
+    // 24h charge history sparkline
     SparklineCanvas {
         anchors.left: parent.left
         anchors.leftMargin: 12
         anchors.right: parent.right
         anchors.rightMargin: 12
-        height: 44
+        height: 32
         history: S.BatteryService.history
-        color: root._stateColor
+        strokeColor: root.accentColor
         active: root.active
-        backgroundTint: 0.07
-        areaMode: true
         thresholds: [
             {
                 value: S.BatteryService.warnThresh,
@@ -160,12 +158,11 @@ Column {
         anchors.rightMargin: 12
         height: 24
         history: S.BatteryService.rateHistory
-        color: root._stateColor
+        strokeColor: root._stateColor
+        colorAt: v => v >= 0 ? S.Theme.base0B : root._stateColor
         active: root.active
         maxValue: null
         minValue: null
-        backgroundTint: 0.08
-        colorFunction: v => v >= 0 ? S.Theme.base0B : root._stateColor
     }
 
     // Health row