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/qmldir

@@ -0,0 +1,2 @@
+# Makes `Theme` a singleton for every file that does `import "."`.
+singleton Theme 1.0 Theme.qml