feat(about): add page for 1956 middle highschool tuition class

This commit introduces a new page dedicated to the 'Middle Highschool Tuition Class' of 1956 (中补班). The page displays a letter written in 2022, calling for a reunion of these special alumni. A navigation
link has been added to the 'About' section for easy access to this historical content.

app/layouts/default.vue

@@ -132,6 +132,13 @@ const items = computed<NavigationMenuItem[]>(() => [
         active: route.path.startsWith("/about/founded-history"),
         icon: "mdi:history",
       },
+      {
+        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",
+        to: "/about/middle-highschool-tuition-class",
+        active: route.path.startsWith("/about/middle-highschool-tuition-class"),
+        icon: "mdi:mail"
+      }
     ],
   },
   {