新增: F-05多模态Phase2a后端(ContentPart+parts字段+provider图片块+truncate防撑爆)

src-tauri/src/commands/ai/title.rs

@@ -50,6 +50,7 @@ pub(crate) async fn ensure_conversation_title(
             .map(|m| ChatMessage {
                 role: m.role.clone(),
                 content: m.content.clone(),
+                parts: None,
                 tool_call_id: None,
                 tool_calls: None,
                 model: None,