feat: add Posts Livewire CRUD page

Adds the Posts index page (list/create/edit/delete) following the
existing Sites/SocialAccounts pattern, and extends the shared nav
layout with a Posts link.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

resources/views/components/layouts/app.blade.php

@@ -11,6 +11,7 @@
     <nav class="bg-white border-b border-gray-200 px-6 py-4 flex gap-6">
         <a href="{{ route('sites.index') }}" class="font-medium hover:text-blue-600">Sites</a>
         <a href="{{ route('social-accounts.index') }}" class="font-medium hover:text-blue-600">Social Accounts</a>
+        <a href="{{ route('posts.index') }}" class="font-medium hover:text-blue-600">Posts</a>
     </nav>
 
     <main class="p-6">