security: remove is_system_role from public API

Remove is_system_role from accept lists in create_role and update_role
actions. This field should only be set via seeds or internal actions to
prevent users from creating unkillable roles through the public API.

lib/accounts/user.ex

@@ -17,6 +17,10 @@ defmodule Mv.Accounts.User do
       # When a member is deleted, set the user's member_id to NULL
       # This allows users to continue existing even if their linked member is removed
       reference :member, on_delete: :nilify
+
+      # When a role is deleted, prevent deletion if users are assigned to it
+      # This protects critical roles from accidental deletion
+      reference :role, on_delete: :restrict
     end
   end
 

lib/mv/authorization/role.ex

@@ -61,14 +61,16 @@ defmodule Mv.Authorization.Role do
 
     create :create_role do
       primary? true
-      accept [:name, :description, :permission_set_name, :is_system_role]
+      # is_system_role is intentionally excluded - should only be set via seeds/internal actions
+      accept [:name, :description, :permission_set_name]
       # Note: In Ash 3.0, require_atomic? is not available for create actions
       # Custom validations will still work
     end
 
     update :update_role do
       primary? true
-      accept [:name, :description, :permission_set_name, :is_system_role]
+      # is_system_role is intentionally excluded - should only be set via seeds/internal actions
+      accept [:name, :description, :permission_set_name]
       # Required because custom validation functions cannot be executed atomically
       require_atomic? false
     end
@@ -85,7 +87,8 @@ defmodule Mv.Authorization.Role do
                Mv.Authorization.PermissionSets.all_permission_sets()
                |> Enum.map(&Atom.to_string/1)
              ),
-             message: "must be one of: own_data, read_only, normal_user, admin"
+             message:
+               "must be one of: #{Mv.Authorization.PermissionSets.all_permission_sets() |> Enum.map_join(", ", &Atom.to_string/1)}"
 
     validate fn changeset, _context ->
                if changeset.data.is_system_role do