JSON Generator for Marii's loot plugin

We need a tool that converts a csv/sheet for loot into a config for Marii's loot plugin! The jsons are easy enough to work with but this is going to scale pretty heavily with the amount of loot we put into the game.

Start by examining how Marii's loot plugin currently represents its JSON configuration and how loot data is maintained in the repository. Define the CSV or spreadsheet input and generated configuration format, then verify that the tool handles the expected loot scale and produces valid plugin configuration.

Written by the indexing model from the issue text.