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/layouts/default.vue

@@ -132,6 +132,12 @@ const items = computed<NavigationMenuItem[]>(() => [
         active: route.path.startsWith("/about/founded-history"),
         icon: "mdi:history",
       },
+      {
+        label: "组织架构",
+        to: "/about/org-structure/20",
+        active: route.path.startsWith("/about/org-structure"),
+        icon: "mdi:account-group",
+      },
       {
         label: "特殊校友：中补班",
         description: "永平中学补习班（1956年）：一封迟来的贴文",