feat(seo): improve SEO and add analytics tracking

This commit introduces several enhancements for SEO and analytics.

- Updates the canonical site URL from `yphsalumni.com` to `yphsalumni.org`.
- Enriches the 'middle-highschool-tuition-class' page with detailed Open Graph (og) meta tags for better social sharing.
- Implements Umami event tracking for the 'Join Us' button on the homepage.

app/pages/index.vue

@@ -39,6 +39,7 @@ const heroCta = ref([
     label: "立即加入我们",
     to: "/join-us",
     icon: "mdi:account-plus",
+    "data-umami-event": "Join Us Btn Click",
   },
 ]);