feat: Add private note action to automations (#11926)

## Summary
- allow AutomationRule to accept `add_private_note` action
- support `add_private_note` in automation action service
- expose private note action in frontend constants and i18n
- test new automation rule action

## Testing
- `pnpm eslint
app/javascript/dashboard/routes/dashboard/settings/automation/constants.js`
- `bundle exec rubocop app/services/automation_rules/action_service.rb
app/models/automation_rule.rb
spec/services/automation_rules/action_service_spec.rb`
- `bundle exec rspec
spec/services/automation_rules/action_service_spec.rb`


------
https://chatgpt.com/codex/tasks/task_e_6870c5f7b8b88326a9bd60b2ba710ccd

Co-authored-by: Muhsin Keloth <muhsinkeramam@gmail.com>

spec/services/automation_rules/action_service_spec.rb

@@ -117,5 +117,27 @@ RSpec.describe AutomationRules::ActionService do
         expect(mailer).to have_received(:conversation_transcript).exactly(1).times
       end
     end
+
+    describe '#perform with add_private_note action' do
+      let(:message_builder) { double }
+
+      before do
+        allow(Messages::MessageBuilder).to receive(:new).and_return(message_builder)
+        rule.actions.delete_if { |a| a['action_name'] == 'send_message' }
+        rule.actions << { action_name: 'add_private_note', action_params: ['Note'] }
+      end
+
+      it 'will add private note' do
+        expect(message_builder).to receive(:perform)
+        described_class.new(rule, account, conversation).perform
+      end
+
+      it 'will not add note if conversation is a tweet' do
+        twitter_inbox = create(:inbox, channel: create(:channel_twitter_profile, account: account))
+        conversation = create(:conversation, inbox: twitter_inbox, additional_attributes: { type: 'tweet' })
+        expect(message_builder).not_to receive(:perform)
+        described_class.new(rule, account, conversation).perform
+      end
+    end
   end
 end