Generates the main router module that delegates to domain-specific routers.

This transformer collects all command-resource mappings from the DSL state and generates:

1. Domain-specific router modules for each domain with commands
2. A main router module that delegates to these domain routers

This transformer should run after the domain router transformer has processed all resources.

Example

# Domain-specific routers
defmodule MyApp.Accounts.Router do
  use Commanded.Commands.Router
  
  dispatch [MyApp.Accounts.Commands.RegisterUser],
    to: MyApp.Accounts.UserAggregate,
    identity: :id
end

defmodule MyApp.Billing.Router do
  use Commanded.Commands.Router
  
  dispatch [MyApp.Billing.Commands.CreateInvoice],
    to: MyApp.Billing.InvoiceAggregate,
    identity: :id
end

# Main router
defmodule MyApp.Router do
  @moduledoc "Main router for all commands in the application"
  
  use Commanded.Commands.Router
  
  # Forward commands to domain-specific routers
  identify MyApp.Accounts.Commands.RegisterUser, as: :accounts
  forward :accounts, to: MyApp.Accounts.Router
  
  identify MyApp.Billing.Commands.CreateInvoice, as: :billing
  forward :billing, to: MyApp.Billing.Router
  
  # Helper function to dispatch any command
  def dispatch_command(command) do
    __MODULE__.dispatch(command)
  end
end

For simpler applications with a single domain, the main router may directly handle commands:

defmodule MyApp.Router do
  use Commanded.Commands.Router
  
  dispatch [MyApp.Commands.RegisterUser, MyApp.Commands.CreateInvoice],
    to: MyApp.UserAggregate,
    identity: :id
end