Related to #825
Add automatic theme switching based on OS preference
* Add logic in `src/mixins/ThemingMixin.js` to detect OS theme preference using `window.matchMedia`.
* Update `initializeTheme` method in `src/mixins/ThemingMixin.js` to set theme based on OS preference.
* Modify `applyLocalTheme` method in `src/mixins/ThemingMixin.js` to apply the detected theme dynamically.
* Include logic in `src/App.vue` to detect and apply theme based on OS preference during app initialization.