chore: mark conversation notifications as read on visit (#13906)

spec/controllers/api/v1/accounts/conversations_controller_spec.rb

@@ -729,6 +729,23 @@ RSpec.describe 'Conversations API', type: :request do
         expect(conversation.reload.assignee_last_seen_at).not_to be_nil
       end
 
+      it 'marks unread notifications as read when updating last seen' do
+        allow(Rails.configuration.dispatcher).to receive(:dispatch)
+        notification = create(:notification, account: account, user: agent, primary_actor: conversation, read_at: nil)
+
+        post "/api/v1/accounts/#{account.id}/conversations/#{conversation.display_id}/update_last_seen",
+             headers: agent.create_new_auth_token,
+             as: :json
+
+        expect(response).to have_http_status(:success)
+        expect(notification.reload.read_at).to be_present
+        expect(Rails.configuration.dispatcher).to have_received(:dispatch).with(
+          'notification.updated',
+          kind_of(Time),
+          hash_including(notification: have_attributes(id: notification.id))
+        )
+      end
+
       it 'throttles updates within an hour when there are no unread messages' do
         conversation.update!(agent_last_seen_at: 30.minutes.ago)
         # Ensure all messages are older than agent_last_seen_at (no unread messages)