feat(web): router with auth guard, AppShell, login + home views

web/src/components/layout/NavBar.vue

@@ -0,0 +1,36 @@
+<template>
+  <header class="border-b border-gray-200 dark:border-gray-700 px-4 py-2 flex items-center gap-4">
+    <h1 class="text-lg font-semibold flex-1">Agent Coding Workflow</h1>
+    <NotificationBell v-if="auth.isAuthenticated" />
+    <NDropdown v-if="auth.user" :options="menu" @select="onSelect">
+      <NButton text>{{ auth.user.display_name }}</NButton>
+    </NDropdown>
+  </header>
+</template>
+
+<script setup lang="ts">
+import { computed } from 'vue'
+import { NButton, NDropdown } from 'naive-ui'
+import { useRouter } from 'vue-router'
+import { useAuthStore } from '@/stores/auth'
+import { authApi } from '@/api/auth'
+import NotificationBell from './NotificationBell.vue'
+
+const auth = useAuthStore()
+const router = useRouter()
+
+const menu = computed(() => [
+  { label: '退出登录', key: 'logout' },
+])
+
+async function onSelect(key: string) {
+  if (key === 'logout') {
+    try {
+      await authApi.logout()
+    } finally {
+      auth.clearSession()
+      router.replace({ name: 'login' })
+    }
+  }
+}
+</script>

web/src/components/layout/NotificationBell.vue

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+<template>
+  <span class="text-sm text-gray-400">🔔</span>
+</template>
+
+<script setup lang="ts">
+// I6 占位：真实未读轮询 + 弹层在 I6 实现。
+</script>