Enhance frontend components and improve authentication handling

Commit notes

- Updated the theme configuration in MantineProvider to include centered modals and pill variant tabs for better UI consistency. - Refactored TransportControls to utilize new icon imports, enhancing visual consistency across the application. - Modified AuthProvider to retrieve the access token instead of the refresh token for improved authentication flow. - Removed unused token getter from AudioEngineProvider and SampleManagementProvider, streamlining the codebase. - Implemented APIClient methods to handle token retrieval and sample downloads more securely. - Updated loaders to utilize tokenManager for authentication, ensuring a more robust token handling mechanism. - Enhanced various routes and components to improve user experience and maintainability.