fix: disable back button when no back path (#936)

Co-authored-by: 三咲智子 Kevin Deng <sxzz@sxzz.moe>

components/nav/NavTitle.vue

@@ -1,5 +1,10 @@
 <script setup lang="ts">
 const { env } = useBuildInfo()
+const router = useRouter()
+const back = ref(router.options.history.state.back)
+router.afterEach(() => {
+  back.value = router.options.history.state.back
+})
 </script>
 
 <template>
@@ -18,7 +23,7 @@ const { env } = useBuildInfo()
         {{ $t('app_name') }} <sup text-sm italic text-secondary mt-1>{{ env === 'release' ? 'alpha' : env }}</sup>
       </div>
     </NuxtLink>
-    <div hidden xl:flex items-center me-8 mt-2>
+    <div hidden xl:flex items-center me-8 mt-2 :class="{ 'pointer-events-none op40': !back }">
       <NuxtLink
         :aria-label="$t('nav.back')"
         @click="$router.go(-1)"