fix: preserve annotaterb output and cover installation config defaults

spec/models/installation_config_spec.rb

@@ -3,5 +3,17 @@
 require 'rails_helper'
 
 RSpec.describe InstallationConfig do
+  subject(:installation_config) { described_class.new(name: 'INSTALLATION_NAME') }
+
   it { is_expected.to validate_presence_of(:name) }
+
+  describe 'new record defaults' do
+    it 'initializes serialized_value with indifferent access' do
+      expect(installation_config.serialized_value).to eq({}.with_indifferent_access)
+    end
+
+    it 'returns nil for value before assignment' do
+      expect(installation_config.value).to be_nil
+    end
+  end
 end