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

TABLES
- Account
  - Struct: Account
  - Fields:
    - Id: ulong (primary key, AutoInc)
    - Email: string (Unique)
    - DisplayName: string

REDUCERS
- CreateAccount(ctx, string email, string displayName)
  - Insert an Account row with the given email and displayName
  - Use Id: 0 for AutoInc
