feat(admin): responsive layout — bottom-tabs auf mobile, sidebar auf desktop

User-Wunsch: kleine screens (iPhone) keine sidebar, sondern bottom-tab-bar
wie native rebreak-app.

Layout-Architektur:
- Desktop (lg+, ≥1024px):
  - Topbar: email + logout-button
  - Sidebar links (w-56) mit full-label-nav (versteckt <lg)
  - Content rechts (p-6)
- Mobile (<lg):
  - Topbar: hamburger UDropdownMenu rechts (email + logout)
  - Sidebar versteckt
  - Content full-width (p-4 pb-24, damit content nicht hinter tab-bar)
  - Bottom-tab-bar: fixed bottom-0, border-t, bg-gray-950/95 backdrop-blur
  - 5 tabs in grid-cols-5: Home / Domains / Users / Stats / Mod
  - Icon (h-5 w-5) + label (text-[10px])
  - Active-state: text-white bg-gray-800 (route-match isActive helper)
  - Safe-area-bottom respektiert via env(safe-area-inset-bottom)

Pages-content unangetastet, nur layout. Build clean.

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

apps/admin/layouts/default.vue

@@ -1,13 +1,15 @@
 <template>
   <div class="min-h-screen bg-gray-950 text-gray-100">
-    <!-- Topbar -->
-    <header class="border-b border-gray-800 bg-gray-900 px-6 py-3 flex items-center justify-between">
+    <!-- Topbar (Desktop + Mobile) -->
+    <header class="border-b border-gray-800 bg-gray-900 px-4 py-3 flex items-center justify-between lg:px-6">
       <div class="flex items-center gap-3">
         <span class="text-sm font-semibold tracking-wide text-gray-400 uppercase">rebreak</span>
         <span class="text-gray-600">/</span>
         <span class="text-sm font-medium text-white">Admin</span>
       </div>
-      <div class="flex items-center gap-4">
+
+      <!-- Desktop: Email + Logout-Button sichtbar -->
+      <div class="hidden lg:flex items-center gap-4">
         <span class="text-xs text-gray-500">{{ adminEmail }}</span>
         <UButton
           size="xs"
@@ -17,11 +19,24 @@
           @click="logout"
         />
       </div>
+
+      <!-- Mobile: Dropdown-Menu fuer Logout/Email -->
+      <UDropdownMenu :items="mobileMenuItems" :popper="{ placement: 'bottom-end' }">
+        <UButton
+          icon="heroicons:bars-3"
+          size="sm"
+          color="neutral"
+          variant="ghost"
+          class="lg:hidden"
+          aria-label="Menu"
+        />
+      </UDropdownMenu>
     </header>
 
-    <!-- Sidebar + Content -->
-    <div class="flex">
-      <aside class="w-56 min-h-[calc(100vh-49px)] border-r border-gray-800 bg-gray-900 py-4">
+    <!-- Sidebar (Desktop) + Content -->
+    <div class="flex flex-col lg:flex-row">
+      <!-- Sidebar nur Desktop -->
+      <aside class="hidden lg:block w-56 min-h-[calc(100vh-49px)] border-r border-gray-800 bg-gray-900 py-4">
         <nav class="flex flex-col gap-1 px-3">
           <NuxtLink
             v-for="item in nav"
@@ -36,21 +51,75 @@
         </nav>
       </aside>
 
-      <main class="flex-1 p-6">
+      <!-- Content -->
+      <main class="flex-1 p-4 lg:p-6 pb-24 lg:pb-6">
         <slot />
       </main>
     </div>
+
+    <!-- Bottom-Tab-Bar (Mobile only) -->
+    <nav
+      class="lg:hidden fixed bottom-0 inset-x-0 z-40 border-t border-gray-800 bg-gray-950/95 backdrop-blur"
+      :style="{ paddingBottom: 'env(safe-area-inset-bottom)' }"
+    >
+      <ul class="grid grid-cols-5">
+        <li v-for="item in nav" :key="item.to">
+          <NuxtLink
+            :to="item.to"
+            class="flex flex-col items-center justify-center gap-1 py-2 text-gray-500 transition-colors"
+            :class="isActive(item.to)
+              ? 'text-white bg-gray-800'
+              : 'hover:text-gray-300'"
+          >
+            <UIcon :name="item.icon" class="h-5 w-5" />
+            <span class="text-[10px] font-medium leading-none">{{ item.shortLabel }}</span>
+          </NuxtLink>
+        </li>
+      </ul>
+    </nav>
   </div>
 </template>
 
 <script setup lang="ts">
 const { adminEmail, logout } = useAdminAuth()
+const route = useRoute()
 
-const nav = [
-  { to: "/", label: "Dashboard", icon: "heroicons:home" },
-  { to: "/domains", label: "Domain-Approval", icon: "heroicons:globe-alt" },
-  { to: "/users", label: "User-Management", icon: "heroicons:users" },
-  { to: "/stats", label: "Statistiken", icon: "heroicons:chart-bar" },
-  { to: "/moderation", label: "Moderation", icon: "heroicons:shield-check" },
+interface NavItem {
+  to: string
+  label: string
+  shortLabel: string
+  icon: string
+}
+
+const nav: NavItem[] = [
+  { to: "/", label: "Dashboard", shortLabel: "Home", icon: "heroicons:home" },
+  { to: "/domains", label: "Domain-Approval", shortLabel: "Domains", icon: "heroicons:globe-alt" },
+  { to: "/users", label: "User-Management", shortLabel: "Users", icon: "heroicons:users" },
+  { to: "/stats", label: "Statistiken", shortLabel: "Stats", icon: "heroicons:chart-bar" },
+  { to: "/moderation", label: "Moderation", shortLabel: "Mod", icon: "heroicons:flag" },
 ]
+
+// Active-State: exact match fuer "/", startsWith fuer Sub-Routes
+function isActive(to: string): boolean {
+  if (to === "/") return route.path === "/"
+  return route.path === to || route.path.startsWith(`${to}/`)
+}
+
+// Mobile-Dropdown-Menu (Header oben rechts)
+const mobileMenuItems = computed(() => [
+  [
+    {
+      label: adminEmail.value || "Admin",
+      icon: "heroicons:user-circle",
+      disabled: true,
+    },
+  ],
+  [
+    {
+      label: "Logout",
+      icon: "heroicons:arrow-right-on-rectangle",
+      onSelect: () => logout(),
+    },
+  ],
+])
 </script>