refactor: Update MainLayout.vue to use Quasar components
This commit refactors the MainLayout.vue file to use Quasar components for the header and layout. The code changes replace the custom header component with a QHeader component and add a QLayout component to improve the overall structure and styling of the layout.
Note: This commit message follows the established convention of using a prefix (refactor
) to indicate code refactoring or restructuring.