Chance Cubes Custom Rewards

The reward pool is data-driven and extendable through JSON files in the config/chancecubes/ folder:

1. Write a reward definition as a JSON file describing what the reward does (items, blocks, entities, structures and so on).
2. For structure-based rewards, capture the structure in-game with /chancecubes schematic and reference the schematic from the reward JSON.
3. Run /chancecubes reload (or restart) - the custom reward joins the pool and can come out of any cube.

Because rewards are plain config files, servers can theme their cube pools - custom loot, custom pranks, custom structures - without writing any code. Reward configs are loaded at boot and survive restarts.