feat(about): add organizational structure page

This commit introduces a new page to display the alumni association's organizational structure.

- Adds a new page at `/about/org-structure` to showcase the committee members.
- Displays each member's photo, position, name, and a brief description of their role.
- The structure is organized into categories: Leadership Team, Functional Departments, and Specialized Departments.
- A navigation link has been added to the main layout sidebar for easy access.

app/pages/about/org-structure.vue

@@ -0,0 +1,16 @@
+<template>
+  <UContainer>
+    <UDashboardToolbar>
+      <UNavigationMenu :items="subPages" />
+    </UDashboardToolbar>
+    <NuxtPage />
+  </UContainer>
+</template>
+
+<script lang="ts" setup>
+import type { NavigationMenuItem } from "@nuxt/ui";
+
+const subPages = ref<NavigationMenuItem[]>([{ label: "20 届", to: "/about/org-structure/20" }]);
+</script>
+
+<style></style>