feat(auth): implement user authentication and email verification

Add registration, login, and logout flows with session management
Integrate Resend for email verification tokens
Create frontend auth views and update topbar state

frontend/src/App.vue

@@ -1,21 +1,80 @@
 <script setup lang="ts">
+import { onMounted, onUnmounted, ref } from 'vue';
+import { useRouter } from 'vue-router';
+import { api, getAuthToken, onAuthTokenChange, setAuthToken, type AuthUser } from './services/api';
+
 const navItems = [
   { label: 'Pokemon', to: '/pokemon' },
   { label: '栖息地', to: '/habitats' },
   { label: '物品 / 材料单', to: '/items' },
   { label: '管理', to: '/admin' }
 ];
+
+const router = useRouter();
+const currentUser = ref<AuthUser | null>(null);
+let removeAuthListener: (() => void) | null = null;
+
+async function loadCurrentUser() {
+  if (!getAuthToken()) {
+    currentUser.value = null;
+    return;
+  }
+
+  try {
+    const response = await api.me();
+    currentUser.value = response.user;
+  } catch {
+    currentUser.value = null;
+    setAuthToken(null);
+  }
+}
+
+async function logout() {
+  try {
+    await api.logout();
+  } catch {
+    // The local session is cleared even when the server session is already gone.
+  }
+
+  currentUser.value = null;
+  setAuthToken(null);
+  await router.push('/pokemon');
+}
+
+onMounted(() => {
+  void loadCurrentUser();
+  removeAuthListener = onAuthTokenChange(() => {
+    void loadCurrentUser();
+  });
+});
+
+onUnmounted(() => {
+  removeAuthListener?.();
+});
 </script>
 
 <template>
   <div class="app-shell">
     <header class="topbar">
-      <RouterLink class="brand" to="/pokemon">Pokopia Wiki</RouterLink>
-      <nav class="nav-tabs" aria-label="主导航">
-        <RouterLink v-for="item in navItems" :key="item.to" :to="item.to">
-          {{ item.label }}
-        </RouterLink>
-      </nav>
+      <div class="topbar-main">
+        <RouterLink class="brand" to="/pokemon">Pokopia Wiki</RouterLink>
+        <nav class="nav-tabs" aria-label="主导航">
+          <RouterLink v-for="item in navItems" :key="item.to" :to="item.to">
+            {{ item.label }}
+          </RouterLink>
+        </nav>
+      </div>
+
+      <div class="auth-actions">
+        <template v-if="currentUser">
+          <span class="auth-user">{{ currentUser.displayName || currentUser.email }}</span>
+          <button class="plain-button" type="button" @click="logout">退出</button>
+        </template>
+        <template v-else>
+          <RouterLink to="/login">登录</RouterLink>
+          <RouterLink to="/register">注册</RouterLink>
+        </template>
+      </div>
     </header>
 
     <main class="page">