fix: 发送消息后清空contenteditable内容

Co-authored-by: Cursor <cursoragent@cursor.com>

components/canvas/CanvasChatPanel.tsx

@@ -529,8 +529,15 @@ export function CanvasChatPanel({ chatId, initialMessages = [], onClose, onOpenF
       parts: parts,
     });
     
+    // 清空状态
     setInput("");
     setAttachments([]);
+    
+    // 🆕 清空 contenteditable div 的内容
+    const editableDiv = textareaRef.current as HTMLDivElement | null;
+    if (editableDiv && editableDiv.isContentEditable) {
+      editableDiv.innerHTML = '';
+    }
   }, [input, attachments, selectedModelId, sendMessage, getRecentImageUrls]);
 
   // 处理文件选择 - 上传后立即添加到画布