feat:将3个文本框默认初始文字改为占位提示语，统一提示文案：请输入

js/script.js

@@ -851,6 +851,28 @@
         let clickStartY = 0;
         let hasMoved = false;
 
+        // 检查是否需要显示 placeholder
+        function updatePlaceholder() {
+            // 获取纯文本内容（排除删除按钮）
+            const textContent = Array.from(element.childNodes)
+                .filter(node => node.nodeType === Node.TEXT_NODE || (node.nodeType === Node.ELEMENT_NODE && !node.classList.contains('text-delete-btn')))
+                .map(node => node.textContent)
+                .join('')
+                .trim();
+            
+            if (!textContent) {
+                element.classList.add('show-placeholder');
+            } else {
+                element.classList.remove('show-placeholder');
+            }
+        }
+        
+        // 初始化时检查
+        updatePlaceholder();
+
+        // 监听输入事件，控制 placeholder 显示
+        element.addEventListener('input', updatePlaceholder);
+
         // 鼠标/触摸按下
         element.addEventListener('mousedown', handleStart);
         element.addEventListener('touchstart', handleStart, { passive: false });
@@ -1083,6 +1105,20 @@
         element.classList.remove('editing');
         element.classList.add('selected');
         element.contentEditable = 'false';
+        
+        // 检查是否需要显示 placeholder
+        const textContent = Array.from(element.childNodes)
+            .filter(node => node.nodeType === Node.TEXT_NODE || (node.nodeType === Node.ELEMENT_NODE && !node.classList.contains('text-delete-btn')))
+            .map(node => node.textContent)
+            .join('')
+            .trim();
+        
+        if (!textContent) {
+            element.classList.add('show-placeholder');
+        } else {
+            element.classList.remove('show-placeholder');
+        }
+        
         element.blur();
         editingInput = null;
         // 隐藏编辑器工具栏