Write a SpacetimeDB backend module in TypeScript that defines an order table and a result table, with a reducer that collects all distinct category values from orders into the result table.

TABLES
- order
  - Fields:
    - id: number (u64, primary key, autoInc)
    - category: string
    - amount: number (u32)

- distinctCategory
  - Fields:
    - category: string (primary key)

REDUCERS
- collect_distinct_categories(ctx)
  - Iterate all orders
  - Collect unique category values (use a Set)
  - Insert each unique category into distinctCategory
