Add admin user management and improve UX

Features:
- Add user management for admins (CRUD operations)
- Add is_admin column to users table
- Add AdminMiddleware for authorization
- Add admin routes and views
- Add artisan command: user:set-admin

Improvements:
- Fix Quick Switcher: add x-data for Alpine.js dispatch
- Fix Quick Switcher: close on outside click
- Redirect non-admin users to front page after login
- Add Knowledge Base link in dashboard navigation
- Change app logo from Laravel to book icon

src/resources/views/layouts/navigation.blade.php

@@ -15,6 +15,12 @@
                     <x-nav-link :href="route('dashboard')" :active="request()->routeIs('dashboard')">
                         {{ __('Dashboard') }}
                     </x-nav-link>
+                    <x-nav-link href="/" :active="false">
+                        <svg class="w-4 h-4 mr-1 inline" fill="none" stroke="currentColor" viewBox="0 0 24 24">
+                            <path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M12 6.042A8.967 8.967 0 006 3.75c-1.052 0-2.062.18-3 .512v14.25A8.987 8.987 0 016 18c2.305 0 4.408.867 6 2.292m0-14.25a8.966 8.966 0 016-2.292c1.052 0 2.062.18 3 .512v14.25A8.987 8.987 0 0018 18a8.967 8.967 0 00-6 2.292m0-14.25v14.25"></path>
+                        </svg>
+                        {{ __('Knowledge Base') }}
+                    </x-nav-link>
                 </div>
             </div>
 
@@ -38,6 +44,12 @@
                             {{ __('Profile') }}
                         </x-dropdown-link>
 
+                        @if(Auth::user()->isAdmin())
+                            <x-dropdown-link :href="route('admin.users.index')">
+                                {{ __('ユーザー管理') }}
+                            </x-dropdown-link>
+                        @endif
+
                         <!-- Authentication -->
                         <form method="POST" action="{{ route('logout') }}">
                             @csrf
@@ -70,6 +82,9 @@
             <x-responsive-nav-link :href="route('dashboard')" :active="request()->routeIs('dashboard')">
                 {{ __('Dashboard') }}
             </x-responsive-nav-link>
+            <x-responsive-nav-link href="/" :active="false">
+                {{ __('Knowledge Base') }}
+            </x-responsive-nav-link>
         </div>
 
         <!-- Responsive Settings Options -->
@@ -84,6 +99,12 @@
                     {{ __('Profile') }}
                 </x-responsive-nav-link>
 
+                @if(Auth::user()->isAdmin())
+                    <x-responsive-nav-link :href="route('admin.users.index')">
+                        {{ __('ユーザー管理') }}
+                    </x-responsive-nav-link>
+                @endif
+
                 <!-- Authentication -->
                 <form method="POST" action="{{ route('logout') }}">
                     @csrf