feat(02-02): create AppFooter, default layout, update app.vue with useLocaleHead

- AppFooter with copyright + Gitea/LinkedIn/Fiverr social icons (rel=noopener noreferrer)
- Default layout wraps header + slot + footer with min-h-screen flex
- app.vue uses NuxtLayout + useLocaleHead for global hreflang/canonical
- Fixed a11y.github -> a11y.gitea in both locale files

app/app.vue

@@ -1,13 +1,16 @@
 <script setup lang="ts">
 const { locale } = useI18n()
+const head = useLocaleHead({ addSeoAttributes: true })
+
 useHead({
   htmlAttrs: { lang: locale },
+  link: computed(() => head.value.link || []),
+  meta: computed(() => head.value.meta || []),
 })
 </script>
 
 <template>
-  <div>
-    <NuxtRouteAnnouncer />
+  <NuxtLayout>
     <NuxtPage />
-  </div>
+  </NuxtLayout>
 </template>