Require auth for the web UI, keep the JSON API open

Sites/Social Accounts/Posts pages now require login; add a Login
Livewire component, guest layout, and logout action. routes/api.php
is untouched, per AI_API.md's documented no-auth-by-design contract.

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

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

@@ -0,0 +1,17 @@
+<!DOCTYPE html>
+<html lang="en">
+<head>
+    <meta charset="utf-8">
+    <meta name="viewport" content="width=device-width, initial-scale=1">
+    <title>{{ $title ?? 'Muninn' }}</title>
+    @vite('resources/css/app.css')
+    @livewireStyles
+</head>
+<body class="bg-gray-50 text-gray-900 flex items-center justify-center min-h-screen">
+    <main class="w-full max-w-sm px-4">
+        {{ $slot }}
+    </main>
+
+    @livewireScripts
+</body>
+</html>