fix(ui): wire up OpenWrtGateway's back button

BackButton is presentational-only (emits click, parent wires navigation)
per its own doc comment, but OpenWrtGateway.vue rendered it with no
@click handler at all -- clicking it did nothing. Added useRouter +
goBack() (-> the 'server' route, matching the page's location under
views/server/), same pattern as PeerFiles.vue/CloudFolder.vue.

Router-detection (openwrt.scan) spot-checked live: RPC plumbing works
end-to-end and returns a valid response, but no physical OpenWrt device
was on hand to confirm a true-positive detection. Also noted:
detect::scan_subnet does blocking TCP/SSH calls inside an async fn with
no .await points -- not proven to cause a real issue yet, but worth
hardening (spawn_blocking or async I/O) before a large subnet scan is
exercised for real.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

neode-ui/src/views/server/OpenWrtGateway.vue

@@ -1,8 +1,14 @@
 <script setup lang="ts">
 import { ref, computed, onMounted } from 'vue'
+import { useRouter } from 'vue-router'
 import { rpcClient } from '@/api/rpc-client'
 import BackButton from '@/components/BackButton.vue'
 
+const router = useRouter()
+function goBack() {
+  router.push({ name: 'server' })
+}
+
 interface ReleaseInfo {
   openwrt_release?: string
   openwrt_version?: string
@@ -363,7 +369,7 @@ onMounted(() => load())
 <template>
   <div class="pb-6">
     <div class="flex items-center gap-3 mb-6">
-      <BackButton />
+      <BackButton @click="goBack" />
       <h1 class="text-lg font-semibold text-white">OpenWrt Gateway</h1>
     </div>