Write a SpacetimeDB backend module in TypeScript that defines a table with a unique constraint on a non-primary-key column and a reducer that inserts rows.

TABLES
- account
  - Fields:
    - id: number (u64, primary key, autoInc)
    - email: string (unique)
    - displayName: string

REDUCERS
- create_account(ctx, { email: string, displayName: string })
  - Insert an account row with the given email and displayName
  - Use id: 0n for autoInc
