Tweaks/cleanups to conversation management in tui

- Pass around message/conversation values instead of pointers where it
makes more sense, and store values instead of pointers in the globally
(within the TUI) shared `App` (pointers provide no utility here).

- Split conversation persistence into separate conversation/message
  saving stages

pkg/tui/views/chat/cmds.go

@@ -36,16 +36,6 @@ func (m *Model) generateConversationTitle() tea.Cmd {
 	}
 }
 
-func (m *Model) updateConversationTitle(conversation *conversation.Conversation) tea.Cmd {
-	return func() tea.Msg {
-		err := m.App.UpdateConversationTitle(conversation)
-		if err != nil {
-			return shared.WrapError(err)
-		}
-		return nil
-	}
-}
-
 func (m *Model) cloneMessage(message conversation.Message, selected bool) tea.Cmd {
 	return func() tea.Msg {
 		msg, err := m.App.CloneMessage(message, selected)
@@ -96,11 +86,21 @@ func (m *Model) cycleSelectedReply(message *conversation.Message, dir model.Mess
 
 func (m *Model) persistConversation() tea.Cmd {
 	return func() tea.Msg {
-		conversation, messages, err := m.App.PersistConversation(m.App.Conversation, m.App.Messages)
+		conversation, err := m.App.PersistConversation()
 		if err != nil {
 			return shared.AsMsgError(err)
 		}
-		return msgConversationPersisted{conversation, messages}
+		return msgConversationPersisted(conversation)
+	}
+}
+
+func (m *Model) persistMessages() tea.Cmd {
+	return func() tea.Msg {
+		messages, err := m.App.PersistMessages()
+		if err != nil {
+			return shared.AsMsgError(err)
+		}
+		return msgMessagesPersisted(messages)
 	}
 }
 
@@ -130,7 +130,7 @@ func (m *Model) promptLLM() tea.Cmd {
 			if err != nil {
 				return msgChatResponseError{Err: err}
 			}
-			return msgChatResponse(resp)
+			return msgChatResponse(*resp)
 		},
 	)
 }