Refactor: Update SimpleUploadButton component and enhance file handling

Commit notes

This commit refactors the `SimpleUploadButton` component to improve file selection and handling for audio uploads. Key changes include:

- **File Selection Logic:** Introduced a new method to filter audio files based on their type and extension, ensuring only valid audio files are processed. - **Folder Upload Support:** Enhanced the component to handle folder uploads, allowing users to select folders containing audio files. - **UI Improvements:** Updated the UI to use a `Menu` for file and folder selection, replacing the previous `Popover` and `Dropzone` implementation for a more streamlined experience. - **Removed Unused Code:** Cleaned up the component by removing unnecessary state management and upload logic, focusing on the file selection aspect.

Additionally, the `LibraryPage` was updated to reflect the new `onFilesSelected` prop for handling selected files.