Feature: defining tools at the resource level

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Is your feature request related to a problem? Please describe.

Tools can only be defined at the domain level, which means tool definitions live far from the actions and policies they relate to. When working on a resource, you have to look at two separate files to understand what's exposed as a tool and how the action is defined.

Describe the solution you'd like

Support tools do block on resources directly, similar to how code_interface supports both domain and resource level definitions. since the resource is implicit, the resource argument could be left out.

defmodule MyApp.HR.Employee do
  use Ash.Resource,
    domain: MyApp.HR,
    authorizers: [Ash.Policy.Authorizer],
    extensions: [AshGrant, AshAi]

  ash_grant do
    resolver MyApp.PermissionResolver
    default_policies true
    default_field_policies true

    scope :all, true
    scope :same_department, expr(department_id == ^actor(:department_id))
    scope :own, expr(id == ^actor(:employee_id))

    field_group :public, [:name, :department, :position, :office_location]
    field_group :hr_basic, [:public], [:phone, :email, :hire_date]
    field_group :payroll, [:hr_basic], [:salary, :bank_account, :tax_id]
  end

  tools do
    tool :search_employees, :read
    tool :update_employee, :update, identity: :id
  end

  actions do
    read :read do
      description "Search employees by name, department, or position"
    end

    update :update do
      accept [:phone, :office_location, :department_id]
      description "Update employee information"
    end
  end
end

An AI agent used be HR gets tools, action, scopes, field-level visibility, and authorization all defined in one place.

Describe alternatives you've considered

Adding a flag like expose_as_tool? true directly on the action would be the simplest option, but per Zach's feedback on Discord, entities (actions/attributes) aren't currently extensible with custom properties.

Additional context

No response