- New src/entities/item/drop_table.rs: DropEntry (chance, min/max count,
pseudo-RNG roll) + DropTable wrapper. grass=5% coin 1-2, rock=10% coin 1,
dirt/air=none.
- New src/entities/shared_systems/digging.rs: Digger component + dig_system.
Any entity with Digger digs the tile below on its interval. Replaces
rabbit_dig_system/rabbit_fall_debug_system/RabbitDigTimer/RabbitFallDebug.
- New TileMap::dig_floor: remove_floor + insert air. Used by dig_system.
- FloorTileData: added drop_table field. Lost Copy derive (Vec field).
Updated all 6 terrain.rs call sites with per-tile drop tables.
- Pig: removed PigDropTimer + pig_drop_system. Drops were debug placeholder.
TODO added for future loot-on-death/butcher system.
- Rabbit: removed all debug components/systems. Now uses Digger::new(5.0).
- main.rs: removed rabbit_dig_system/rabbit_fall_debug_system/pig_drop_system,
added shared_systems::digging::dig_system.
