Title: [Feature Request] Support `@@schema` for multi-schema database organization

[dhritcu]

It would be helpful if ZenStack v3 supported a @@schema model-level attribute, similar to Zenstack v2 implementation, to allow placing tables in specific PostgreSQL schemas.

Example:

model Address {
  id    String @id @default(uuid())
  city  String
  @@map("addresses")
  @@schema("inventory")
}

Expected behavior:
• The generated SQL and client accessors should respect the schema during CRUD operations.
• Should work with existing @@map and relation directives seamlessly.

[ymc9]

added in beta.21
https://zenstack.dev/docs/3.x/recipe/postgres-multi-schema