🥗🧹 Tobias: Trust#destroy destroys Trust#beneficiaries

Again, we may want to leverage an archival system rather than
destruction, but for now let's make sure we clean up when a `Trust` is
detroyed.

app/furniture/tobias/trust.rb

@@ -2,6 +2,6 @@ class Tobias
   class Trust < ApplicationRecord
     self.table_name = "tobias_trusts"
 
-    has_many :beneficiaries
+    has_many :beneficiaries, inverse_of: :trust, dependent: :destroy
   end
 end

spec/tobias/trust_spec.rb

@@ -0,0 +1,7 @@
+require "rails_helper"
+
+RSpec.describe Tobias::Trust, type: :model do
+  describe "#benficiaries" do
+    it { is_expected.to have_many(:beneficiaries).inverse_of(:trust).dependent(:destroy) }
+  end
+end