refactor: enhance TimerPage layout and functionality; update theme and tokens for improved design consistency

- Refactored TimerPage component to improve layout and user experience.
- Updated theme configuration to utilize design tokens for better maintainability.
- Introduced new tokens for colors and typography to align with design principles.
- Simplified state management and improved timer functionality.
- Enhanced accessibility and responsiveness of UI elements.

desktop/kadence_desktop/qml/components/Panel.qml

@@ -0,0 +1,28 @@
+// A surface with a hairline border. No shadow, no tint — the border does the
+// separating, which is what keeps a page of panels calm.
+import QtQuick
+import QtQuick.Layouts
+
+import ".."
+
+Rectangle {
+    id: panel
+    default property alias content: inner.data
+    property int padding: Theme.pad
+    property alias spacing: inner.spacing
+
+    color: Theme.surface
+    radius: Theme.radius
+    border.width: 1
+    border.color: Theme.rule
+    implicitHeight: inner.implicitHeight + padding * 2
+    implicitWidth: inner.implicitWidth + padding * 2
+    Layout.fillWidth: true
+
+    ColumnLayout {
+        id: inner
+        anchors.fill: parent
+        anchors.margins: panel.padding
+        spacing: 10
+    }
+}