test: 补充侧边栏滚动位置持久化的前端测试

- AppSidebar.spec.ts：验证 template ref 绑定、sidebarNavRef 声明、
  onBeforeUnmount 保存 scrollTop、onMounted 恢复
- app.spec.ts：验证 sidebarScrollTop 默认值为 0 且可读写

frontend/src/components/layout/__tests__/AppSidebar.spec.ts

@@ -19,6 +19,29 @@ describe('AppSidebar custom SVG styles', () => {
   })
 })
 
+describe('AppSidebar scroll position persistence', () => {
+  it('binds a template ref to the sidebar nav element', () => {
+    expect(componentSource).toContain('ref="sidebarNavRef"')
+    expect(componentSource).toContain('sidebar-nav')
+  })
+
+  it('declares sidebarNavRef in script setup', () => {
+    expect(componentSource).toContain("const sidebarNavRef = ref<HTMLElement | null>(null)")
+  })
+
+  it('saves scroll position on beforeUnmount', () => {
+    expect(componentSource).toContain('onBeforeUnmount')
+    expect(componentSource).toContain('appStore.sidebarScrollTop')
+    expect(componentSource).toContain('sidebarNavRef.value.scrollTop')
+  })
+
+  it('restores scroll position on mount', () => {
+    expect(componentSource).toContain('onMounted')
+    expect(componentSource).toContain('appStore.sidebarScrollTop')
+    expect(componentSource).toContain('nextTick')
+  })
+})
+
 describe('AppSidebar header styles', () => {
   it('does not clip the version badge dropdown', () => {
     const sidebarHeaderBlockMatch = styleSource.match(/\.sidebar-header\s*\{[\s\S]*?\n {2}\}/)