feat(app): 编辑器增强 — 查看模式 + 图层排序 + 标签/贴纸动态化

- EditorPage 新增查看模式: 打开已保存日记默认只读，编辑按钮切换
- EditorBloc 新增 ElementLayerChanged 事件，支持置顶/置底图层排序
- DraggableElement 添加图层控制按钮 (置顶/置底/删除)
- TagPanel 标签建议改为从日记历史动态生成 (Top 10 频率)
- StickerPickerSheet 重构，预留 API 扩展点

app/lib/features/editor/widgets/draggable_element.dart

@@ -12,6 +12,7 @@ import 'dart:io';
 import 'package:flutter/material.dart';
 
 import '../../../data/models/journal_element.dart';
+import '../bloc/editor_bloc.dart' show LayerChange;
 
 /// 可拖拽日记元素组件
 class DraggableElement extends StatefulWidget {
@@ -22,6 +23,7 @@ class DraggableElement extends StatefulWidget {
   final void Function(String id, double w, double h)? onResized;
   final void Function(String id, double rotation)? onRotated;
   final ValueChanged<String> onDeleted;
+  final void Function(String id, LayerChange change)? onLayerChanged;
 
   const DraggableElement({
     super.key,
@@ -32,6 +34,7 @@ class DraggableElement extends StatefulWidget {
     this.onResized,
     this.onRotated,
     required this.onDeleted,
+    this.onLayerChanged,
   });
 
   @override
@@ -142,26 +145,41 @@ class _DraggableElementState extends State<DraggableElement> {
                 ),
               ),
 
-              // 选中时显示删除按钮
+              // 选中时显示操作按钮：图层 + 删除
               if (widget.isSelected)
                 Positioned(
                   top: -12,
                   right: -12,
-                  child: GestureDetector(
-                    onTap: () => widget.onDeleted(widget.element.id),
-                    child: Container(
-                      width: 24,
-                      height: 24,
-                      decoration: BoxDecoration(
+                  child: Row(
+                    mainAxisSize: MainAxisSize.min,
+                    children: [
+                      // 置顶
+                      _ActionButton(
+                        icon: Icons.flip_to_front_rounded,
+                        color: Theme.of(context).colorScheme.primary,
+                        onTap: () => widget.onLayerChanged?.call(
+                          widget.element.id,
+                          LayerChange.bringToFront,
+                        ),
+                      ),
+                      const SizedBox(width: 4),
+                      // 置底
+                      _ActionButton(
+                        icon: Icons.flip_to_back_rounded,
+                        color: Theme.of(context).colorScheme.primary,
+                        onTap: () => widget.onLayerChanged?.call(
+                          widget.element.id,
+                          LayerChange.sendToBack,
+                        ),
+                      ),
+                      const SizedBox(width: 4),
+                      // 删除
+                      _ActionButton(
+                        icon: Icons.close_rounded,
                         color: Theme.of(context).colorScheme.error,
-                        shape: BoxShape.circle,
+                        onTap: () => widget.onDeleted(widget.element.id),
                       ),
-                      child: const Icon(
-                        Icons.close_rounded,
-                        size: 16,
-                        color: Colors.white,
-                      ),
-                    ),
+                    ],
                   ),
                 ),
             ],
@@ -279,3 +297,32 @@ class _DraggableElementState extends State<DraggableElement> {
     );
   }
 }
+
+/// 选中元素的操作按钮（图层/删除）
+class _ActionButton extends StatelessWidget {
+  final IconData icon;
+  final Color color;
+  final VoidCallback onTap;
+
+  const _ActionButton({
+    required this.icon,
+    required this.color,
+    required this.onTap,
+  });
+
+  @override
+  Widget build(BuildContext context) {
+    return GestureDetector(
+      onTap: onTap,
+      child: Container(
+        width: 24,
+        height: 24,
+        decoration: BoxDecoration(
+          color: color,
+          shape: BoxShape.circle,
+        ),
+        child: Icon(icon, size: 16, color: Colors.white),
+      ),
+    );
+  }
+}