refactor(auth): AuthLayout supports optional narrative slot

New slot 'narrative' enables split-screen layout (50/50 desktop, collapses
to single column on mobile <900px).

Backward compatibility:
- Pages that don't pass a narrative slot still render the original
  centered-card layout with siteName + logo + copyright
- ForgotPassword, ResetPassword, EmailVerify unaffected

To be used in Tasks 8 and 9 (LoginView, RegisterView).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/src/components/layout/AuthLayout.vue

@@ -1,69 +1,45 @@
 <template>
-  <div class="relative flex min-h-screen items-center justify-center overflow-hidden p-4">
+  <div class="auth-shell" :class="{ 'auth-shell-split': hasNarrative }">
-    <!-- Background -->
+    <div class="bg-glow soft"></div>
-    <div
-      class="absolute inset-0 bg-gradient-to-br from-gray-50 via-primary-50/30 to-gray-100 dark:from-dark-950 dark:via-dark-900 dark:to-dark-950"
-    ></div>
 
-    <!-- Decorative Elements -->
+    <!-- LEFT: Narrative (split mode only, hidden on mobile) -->
-    <div class="pointer-events-none absolute inset-0 overflow-hidden">
+    <aside v-if="hasNarrative" class="auth-narrative">
-      <!-- Gradient Orbs -->
+      <slot name="narrative"></slot>
-      <div
+    </aside>
-        class="absolute -right-40 -top-40 h-80 w-80 rounded-full bg-primary-400/20 blur-3xl"
-      ></div>
-      <div
-        class="absolute -bottom-40 -left-40 h-80 w-80 rounded-full bg-primary-500/15 blur-3xl"
-      ></div>
-      <div
-        class="absolute left-1/2 top-1/2 h-96 w-96 -translate-x-1/2 -translate-y-1/2 rounded-full bg-primary-300/10 blur-3xl"
-      ></div>
 
-      <!-- Grid Pattern -->
+    <!-- RIGHT: Form -->
-      <div
+    <main class="auth-main">
-        class="absolute inset-0 bg-[linear-gradient(rgba(20,184,166,0.03)_1px,transparent_1px),linear-gradient(90deg,rgba(20,184,166,0.03)_1px,transparent_1px)] bg-[size:64px_64px]"
+      <div class="auth-main-inner">
-      ></div>
+        <!-- Legacy centered-card header (only when no narrative slot) -->
-    </div>
+        <div class="mb-8 text-center" v-if="!hasNarrative && settingsLoaded">
-
-    <!-- Content Container -->
-    <div class="relative z-10 w-full max-w-md">
-      <!-- Logo/Brand -->
-      <div class="mb-8 text-center">
-        <!-- Custom Logo or Default Logo -->
-        <template v-if="settingsLoaded">
           <div
-            class="mb-4 inline-flex h-16 w-16 items-center justify-center overflow-hidden rounded-2xl shadow-lg shadow-primary-500/30"
+            class="mb-4 inline-flex h-14 w-14 items-center justify-center overflow-hidden rounded-2xl"
           >
             <img :src="siteLogo || '/logo.png'" alt="Logo" class="h-full w-full object-contain" />
           </div>
-          <h1 class="text-gradient mb-2 text-3xl font-bold">
+          <h1 class="text-2xl font-bold">{{ siteName }}</h1>
-            {{ siteName }}
+          <p class="text-sm text-gray-500 dark:text-dark-400" v-if="siteSubtitle">{{ siteSubtitle }}</p>
-          </h1>
+        </div>
-          <p class="text-sm text-gray-500 dark:text-dark-400">
-            {{ siteSubtitle }}
-          </p>
-        </template>
-      </div>
 
-      <!-- Card Container -->
+        <!-- Form content -->
-      <div class="card-glass rounded-2xl p-8 shadow-glass">
         <slot />
-      </div>
 
-      <!-- Footer Links -->
+        <!-- Footer link slot (e.g., "没有账户？注册") -->
-      <div class="mt-6 text-center text-sm">
+        <div class="mt-6 text-center text-sm">
-        <slot name="footer" />
+          <slot name="footer" />
-      </div>
+        </div>
 
-      <!-- Copyright -->
+        <!-- Copyright (legacy mode only) -->
-      <div class="mt-8 text-center text-xs text-gray-400 dark:text-dark-500">
+        <div class="mt-8 text-center text-xs text-gray-400 dark:text-dark-500" v-if="!hasNarrative">
-        &copy; {{ currentYear }} {{ siteName }}. All rights reserved.
+          &copy; {{ currentYear }} {{ siteName }}. All rights reserved.
+        </div>
       </div>
-    </div>
+    </main>
   </div>
 </template>
 
 <script setup lang="ts">
-import { computed, onMounted } from 'vue'
+import { computed, onMounted, useSlots } from 'vue'
 import { useAppStore } from '@/stores'
 import { sanitizeUrl } from '@/utils/url'
 
@@ -76,6 +52,9 @@ const settingsLoaded = computed(() => appStore.publicSettingsLoaded)
 
 const currentYear = computed(() => new Date().getFullYear())
 
+const slots = useSlots()
+const hasNarrative = computed(() => !!slots.narrative)
+
 onMounted(() => {
   appStore.fetchPublicSettings()
 })
@@ -85,4 +64,57 @@ onMounted(() => {
 .text-gradient {
   @apply bg-gradient-to-r from-primary-600 to-primary-500 bg-clip-text text-transparent;
 }
+
+.auth-shell {
+  min-height: 100vh;
+  position: relative;
+  overflow: hidden;
+}
+.auth-shell-split {
+  display: grid;
+  grid-template-columns: 1fr 1fr;
+}
+@media (max-width: 900px) {
+  .auth-shell-split {
+    grid-template-columns: 1fr;
+  }
+  .auth-narrative {
+    display: none;
+  }
+}
+.auth-narrative {
+  position: relative;
+  padding: 48px 56px;
+  background: linear-gradient(135deg, #0a0e1a 0%, #1e1b4b 100%);
+  border-right: 1px solid var(--border);
+  display: flex;
+  flex-direction: column;
+  justify-content: space-between;
+  color: var(--text-0);
+  font-family: var(--font-sans);
+}
+.auth-main {
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  padding: 40px 24px;
+  position: relative;
+  z-index: 2;
+}
+.auth-main-inner {
+  width: 100%;
+  max-width: 420px;
+}
+
+/* Legacy-mode (no narrative slot) background — keep existing gradient decorative look */
+.auth-shell:not(.auth-shell-split) {
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  padding: 1rem;
+  background: linear-gradient(to bottom right, #f9fafb, rgba(240,253,250,0.3), #f3f4f6);
+}
+:global(.dark) .auth-shell:not(.auth-shell-split) {
+  background: linear-gradient(to bottom right, #020617, #0f172a, #020617);
+}
 </style>