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/PageHeader.qml

@@ -0,0 +1,55 @@
+// Eyebrow, title, actions, rule — the same opening every page uses.
+import QtQuick
+import QtQuick.Controls
+import QtQuick.Layouts
+
+import ".."
+
+ColumnLayout {
+    property string eyebrow: ""
+    property string title: ""
+    property string caption: ""
+    default property alias actions: actionRow.data
+
+    Layout.fillWidth: true
+    spacing: 10
+
+    RowLayout {
+        Layout.fillWidth: true
+        spacing: 16
+
+        ColumnLayout {
+            Layout.fillWidth: true
+            spacing: 2
+            Label {
+                visible: eyebrow !== ""
+                text: eyebrow.toUpperCase()
+                color: Theme.muted
+                font.pixelSize: 10
+                font.letterSpacing: 1.3
+                font.weight: Font.DemiBold
+                font.family: Theme.sansFamily
+            }
+            Label {
+                text: title
+                color: Theme.ink
+                font.pixelSize: 27
+                font.family: Theme.displayFamily
+                font.letterSpacing: -0.6
+            }
+            Label {
+                visible: caption !== ""
+                text: caption
+                color: Theme.muted
+                font.pixelSize: 13
+                font.family: Theme.sansFamily
+                Layout.fillWidth: true
+                wrapMode: Text.WordWrap
+            }
+        }
+
+        RowLayout { id: actionRow; spacing: 8; Layout.alignment: Qt.AlignRight | Qt.AlignVCenter }
+    }
+
+    Rectangle { Layout.fillWidth: true; height: 1; color: Theme.rule }
+}