Add authentication, a public landing page, and guest data preview

Hand-rolled login/register/logout on Laravel's built-in Auth facade
rather than Breeze/Jetstream, which scaffold Tailwind v3 config and
would fight our existing Tailwind v4 CSS-first setup. Login/Register
are Livewire components; logout is a plain POST route (auth-gated,
CSRF-protected).

Routing: "/" is now a public landing page describing the project;
the sites list moved from "/" to "/sites" to make room for it.

Data gating: App\Support\GuestPreview::paginate() forces page 1 and a
5-row page size for unauthenticated visitors on Sites, Discover, and
a site's Pages/Backlinks tables, while total() still reflects the
real match count — authenticated users get the existing full
pagination unchanged. A shared guest-preview-notice component shows
"N of M results, sign in to see all" and only renders when something
is actually being hidden.

Testing: pointed the test suite at a dedicated MySQL database
(huginn_testing) instead of the default in-memory SQLite, since the
existing fulltext index migration isn't SQLite-compatible — this app
is MySQL-specific by now regardless. Added AuthFlowTest (register,
login, wrong-password rejection, logout) and GuestPreviewTest (guest
capped to a preview, authenticated sees everything), all passing.

Also fixed a real bug the tests caught: request()->session() isn't
reliably attached during Livewire's in-process test action calls;
switched Login/Register to the session() helper, which resolves the
session store directly and works in both contexts.

app/Http/Controllers/SiteController.php

@@ -3,18 +3,20 @@
 namespace App\Http\Controllers;
 
 use App\Models\Site;
+use App\Support\GuestPreview;
 use Illuminate\Contracts\View\View;
 
 class SiteController extends Controller
 {
     public function show(Site $site): View
     {
-        $pages = $site->pages()->orderBy('url')->paginate(50, ['*'], 'pages_page');
+        $pages = GuestPreview::paginate($site->pages()->orderBy('url'), 50, 'pages_page');
 
-        $backlinks = $site->inboundLinks()
-            ->with(['site', 'sitePage'])
-            ->latest()
-            ->paginate(50, ['*'], 'backlinks_page');
+        $backlinks = GuestPreview::paginate(
+            $site->inboundLinks()->with(['site', 'sitePage'])->latest(),
+            50,
+            'backlinks_page'
+        );
 
         $referringDomainsCount = $site->inboundLinks()->distinct()->count('site_id');
         $outboundLinksCount = $site->outboundLinks()->count();