feat: phase 1C JWT UI, events/hosts API, Vue frontend

Co-authored-by: Cursor <cursoragent@cursor.com>

frontend/src/App.vue

@@ -0,0 +1,27 @@
+<template>
+  <div class="layout">
+    <nav v-if="showNav">
+      <span class="brand">SAC</span>
+      <RouterLink to="/events">События</RouterLink>
+      <RouterLink to="/hosts">Хосты</RouterLink>
+      <button type="button" class="secondary" @click="logout">Выход</button>
+    </nav>
+    <RouterView />
+  </div>
+</template>
+
+<script setup lang="ts">
+import { computed } from "vue";
+import { useRoute, useRouter } from "vue-router";
+import { clearToken, getToken } from "./api";
+
+const route = useRoute();
+const router = useRouter();
+
+const showNav = computed(() => route.path !== "/login" && !!getToken());
+
+function logout() {
+  clearToken();
+  router.push("/login");
+}
+</script>