Better handling of newly saved conversations

When a new conversation is created in the chat view's
`persistConversation`, we now set `rootMessages` appropriately.

pkg/tui/views/chat/chat.go

@@ -35,6 +35,7 @@ type (
 	msgMessagesLoaded []models.Message
 	// sent when the conversation has been persisted, triggers a reload of contents
 	msgConversationPersisted struct {
+		isNew        bool
 		conversation *models.Conversation
 		messages     []models.Message
 	}