feat: delete converters and explorers

[Irozuku]

This pull request introduces backend and frontend support for deleting converters (and related items) and explorers from notebooks, along with UI improvements for managing converters and explorers. The backend adds a new API endpoint to delete a converter and all subsequent converters and explorers, while the frontend provides delete buttons and confirmation dialogs for these actions. Additionally, the codebase is refactored to improve modularity and maintainability, especially around job queue logic and schema definitions.

Backend: Converter Deletion and Refactoring

• Added a new DELETE /{converter_list_id} endpoint in converters.py to delete a converter list and all subsequent converters and explorers, restore the original dataset, and re-enqueue previous converters as jobs.
• Moved ConverterParams and ConverterListParams Pydantic models into a new converter_params.py schema file, updating imports accordingly for better separation of concerns. [1] [2] [3]
• Refactored job queue logic by extracting core job enqueueing into a reusable _enqueue_job_logic function, reducing code duplication in jobs.py. [1] [2] [3]

Frontend: UI Enhancements for Deletion

• Added delete buttons to converter and explorer UI components (ConverterBox, ExplorerBox, ConverterHistoryList) and implemented a new ItemsToDeleteList component to display which items will be deleted. [1] [2] [3] [4] [5] [6] [7] [8] [9]
• Added a new API function deleteConverterById to support deletion from the frontend.

General Improvements

• Updated modal and dialog components to use React hooks for improved interactivity and state management.

These changes collectively enable users to safely and efficiently manage (including delete) converter and explorer histories from both backend and frontend, with improved code structure and maintainability.