Write a SpacetimeDB backend module in C# that defines a User table and a stats table, with a reducer that counts total users and active users without collecting into a list.

TABLES
- User
  - Struct: User
  - Fields:
    - Id: ulong (primary key, AutoInc)
    - Name: string
    - Active: bool

- UserStats
  - Struct: UserStats
  - Fields:
    - Key: string (primary key)
    - Count: ulong

REDUCERS
- ComputeUserCounts(ctx)
  - Count total users by iterating (do not collect into a List first)
  - Count active users by iterating and checking Active == true
  - Insert a UserStats row with Key="total" and the total count
  - Insert a UserStats row with Key="active" and the active count
