feat(seo): implement SEO enhancements and social media embeds

This commit introduces significant SEO improvements and enhances content embedding capabilities.

- Integrates `@nuxtjs/seo`, `@nuxtjs/sitemap`, and `@nuxtjs/robots` to boost search engine visibility.
- Configures global meta tags, including Open Graph and Twitter Cards, for richer social media sharing.
- Adds support for embedding YouTube and Facebook content directly within markdown pages.
- Introduces a new `TikTokEmbed` component for future use.

nuxt.config.ts

@@ -4,13 +4,22 @@ import tailwindcss from "@tailwindcss/vite";
 export default defineNuxtConfig({
   compatibilityDate: "2025-07-15",
   devtools: { enabled: true },
-  modules: ["@nuxt/content", "@nuxt/image", "@nuxt/ui", "reka-ui/nuxt"],
+  modules: [
+    "@nuxt/content",
+    "@nuxt/image",
+    "@nuxt/ui",
+    "reka-ui/nuxt",
+    "@nuxtjs/robots",
+    "@nuxtjs/seo",
+    "@nuxtjs/sitemap",
+  ],
   css: ["~/assets/css/main.css"],
   vite: {
     plugins: [tailwindcss()],
   },
   app: {
     head: {
+      titleTemplate: "%s - 永平中学校友会",
       title: "永平中学校友会",
       script: [
         {
@@ -18,6 +27,30 @@ export default defineNuxtConfig({
           tagPosition: "head",
         },
       ],
+      meta: [
+        // 基础 SEO
+        { name: "description", content: "永平中学校友会官网 - 连接校友，共享资源，传承母校精神。" },
+        { name: "keywords", content: "永平中学, 校友会, 永平中学校友, 永平校友, 同学会" },
+        { name: "author", content: "永平中学校友会" },
+        { name: "viewport", content: "width=device-width, initial-scale=1" },
+
+        // Open Graph（Facebook/LinkedIn）
+        { property: "og:title", content: "永平中学校友会" },
+        { property: "og:description", content: "永平中学校友会官网 - 连接校友，共享资源，传承母校精神。" },
+        { property: "og:type", content: "website" },
+        { property: "og:url", content: "https://yphsalumni.org" }, // ✅ 换成你网站的真实域名
+        { property: "og:image", content: "https://yphsalumni.org/hero-image.jpg" }, // ✅ 上传一张封面图
+
+        // Twitter Card
+        { name: "twitter:card", content: "summary_large_image" },
+        { name: "twitter:title", content: "永平中学校友会" },
+        { name: "twitter:description", content: "连接校友，共享资源，传承母校精神。" },
+        { name: "twitter:image", content: "https://yphsalumni.org/hero-image.jpg" },
+      ],
     },
   },
-});
+  site: {
+    url: "https://yphsalumni.com",
+    name: "永中校友会 YPHS Alumni"
+  }
+});