fix(gui): remove TextEdit color property for syntax highlighting

Qt5's TextEdit 'color' property can override inline styles from RichText,
breaking syntax highlighting colors. Remove the property so inline color
spans from KSyntaxHighlighting are respected.

Default text color should come from the application palette.

gui/main.qml

@@ -930,7 +930,8 @@ property bool blockExpanded: {
             wrapMode: TextEdit.Wrap
             font.family: theme.fontFamily || Qt.application.font.family
             font.pointSize: theme.fontSize > 0 ? theme.fontSize : 12
-            color: theme.textColor
+            // Note: don't set 'color' here — it can override inline styles from
+            // syntax highlighting in Qt5. The HTML content should set colors.
         }
                     }
                 }