fix: 任务栏 ↑↓ 箭头颜色跟随字体颜色设置

- 横向/竖向布局共 4 处箭头 Text 的 color 从 root.secondaryText
  改为 root.speedTextColor，与网速数值统一受 textColor 属性控制
- 弹窗详情的标签色（secondaryText）保持不变，不受字体颜色设置影响

package/networkview.qml

@@ -158,7 +158,7 @@ AppletItem {
             Text {
                 text: "↓"
                 font.pixelSize: root.dockSize * 0.20
-                color: root.secondaryText
+                color: root.speedTextColor
                 Layout.alignment: Qt.AlignVCenter
             }
 
@@ -179,7 +179,7 @@ AppletItem {
             Text {
                 text: "↑"
                 font.pixelSize: root.dockSize * 0.20
-                color: root.secondaryText
+                color: root.speedTextColor
                 Layout.alignment: Qt.AlignVCenter
             }
 
@@ -212,7 +212,7 @@ AppletItem {
             Text {
                 text: "↓"
                 font.pixelSize: root.dockSize * 0.20
-                color: root.secondaryText
+                color: root.speedTextColor
                 anchors.horizontalCenter: parent.horizontalCenter
             }
 
@@ -239,7 +239,7 @@ AppletItem {
             Text {
                 text: "↑"
                 font.pixelSize: root.dockSize * 0.20
-                color: root.secondaryText
+                color: root.speedTextColor
                 anchors.horizontalCenter: parent.horizontalCenter
             }