Revamps the entire user deletion process to resolve critical performance bottlenecks that caused the web panel and database to freeze when removing multiple users.
- **Backend:** Core scripts (`kickuser.py`, `remove_user.py`) and the database layer are re-engineered to handle multiple users in a single, efficient batch operation using MongoDB's `delete_many`.
- **API:** A new `POST /api/v1/users/bulk-delete` endpoint is introduced for batch removals. The existing single-user `DELETE` endpoint is fixed to align with the new bulk logic.
- **Frontend:** The Users page now intelligently calls the bulk API when multiple users are selected, drastically improving UI responsiveness and reducing server load.
