feat: add frontend admin shortcut for staff

Let admin and editor open /admin in a new tab from the public header and profile, so they can jump to the backend without leaving the site.

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

resources/views/partials/admin-link.blade.php

@@ -0,0 +1,9 @@
+@auth
+    @if(auth()->user()->canAccessAdmin())
+        @if(! empty($asList))
+            <li><a href="{{ url('/admin') }}" target="_blank" rel="noopener">管理</a></li>
+        @else
+            <a href="{{ url('/admin') }}" target="_blank" rel="noopener">管理</a>
+        @endif
+    @endif
+@endauth

resources/views/partials/header.blade.php

@@ -18,6 +18,7 @@
             </form>
             @auth
                 <a href="{{ route('profile') }}">{{ auth()->user()->name }}</a>
+                @include('partials.admin-link')
                 <form action="{{ route('logout') }}" method="post" class="inline-form">
                     @csrf
                     <button type="submit" class="link-btn">退出</button>