Implemented backend API and frontend UI for importing local plugin zip files. The backend now supports file uploads via a new /Plugin/Import endpoint using multer, and the frontend provides a button to upload and import plugins directly from the dashboard.
Prompt to register plugin manager if not loaded
Renames plugin_develop.ts to plugin-develop.ts for consistency. Updates the plugin import handler to prompt the user to register the plugin manager if it is not loaded, improving user experience and error handling.
