refactor(editor): 优化条件渲染逻辑减少代码行数

- 将选中状态条件渲染的换行写法合并为单行表达式
- 精简类名绑定代码，提升代码可读性
- 保持功能逻辑不变，仅优化代码结构和格式

src/views/editor/components/DocNodeRenderer/index.vue

@@ -140,9 +140,7 @@
                                 contenteditable="true"
                                 class="focus:outline-none px-0.5 rounded inline transition-all whitespace-pre-wrap focus:bg-fill-3"
                                 :class="[
-                                    editorStore.selectedNodeId === `${node.id}-txt-${index}`
-                                        ? 'ring-2 ring-primary ring-offset-1 bg-primary/10'
-                                        : ''
+                                    editorStore.selectedNodeId === `${node.id}-txt-${index}` ? 'ring-2 ring-primary ring-offset-1 bg-primary/10' : ''
                                 ]"
                                 @click.stop="editorStore.setSelectedNodeId(`${node.id}-txt-${index}`)"
                                 @blur="handleMixedTextBlur(index, $event)"
@@ -156,9 +154,7 @@
                                 :contenteditable="false"
                                 class="focus:outline-none px-0.5 rounded inline transition-all whitespace-pre-wrap"
                                 :class="[
-                                    editorStore.selectedNodeId === `${node.id}-txt-${index}`
-                                        ? 'ring-2 ring-primary ring-offset-1 bg-primary/10'
-                                        : ''
+                                    editorStore.selectedNodeId === `${node.id}-txt-${index}` ? 'ring-2 ring-primary ring-offset-1 bg-primary/10' : ''
                                 ]"
                                 @click.stop="editorStore.setSelectedNodeId(`${node.id}-txt-${index}`)"
                             >