refactor(ui): consolidate Theme.qml tokens and replace unicode glyphs with SVG icons

src/pygui/ISC/Tabs/components/ReadoutPanel.qml

@@ -1,5 +1,6 @@
 import QtQuick
 import QtQuick.Controls
+import QtQuick.Controls.impl
 import QtQuick.Layouts
 import ISC
 
@@ -32,18 +33,17 @@ ColumnLayout {
                 ColorAnimation { duration: Theme.durationFast }
             }
 
-            Text {
+            IconImage {
                 anchors.centerIn: parent
-                text: "✓"
-                font.pixelSize: Theme.fontSm
-                font.bold: true
+                source: "../icons/check.svg"
+                width: 12; height: 12
+                sourceSize.width: 12
+                sourceSize.height: 12
                 color: Theme.panelBackground
                 opacity: toggle.checked ? 1.0 : 0.0
                 Behavior on opacity {
                     NumberAnimation { duration: Theme.durationFast }
                 }
-                verticalAlignment: Text.AlignVCenter
-                horizontalAlignment: Text.AlignHCenter
             }
         }
 
@@ -205,7 +205,7 @@ ColumnLayout {
                 Item { Layout.fillWidth: true }
                 Label {
                     text: s.diff !== undefined ? s.diff : "—"
-                    color: Theme.isDarkMode ? "#A78BFA" : "#8B5CF6"
+                    color: Theme.diffAccent
                     font.family: Theme.codeFontFamily
                     font.pixelSize: Theme.fontMd
                     font.bold: true