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/Livewire/Sites/Index.php

@@ -3,6 +3,7 @@
 namespace App\Livewire\Sites;
 
 use App\Models\Site;
+use App\Support\GuestPreview;
 use Illuminate\Contracts\View\View;
 use Livewire\Attributes\Layout;
 use Livewire\Attributes\Url;
@@ -24,14 +25,15 @@ class Index extends Component
 
     public function render(): View
     {
-        $sites = Site::query()
-            ->withCount('pages')
-            ->when(
-                $this->search !== '',
-                fn ($query) => $query->where('domain', 'like', '%'.$this->search.'%')
-            )
-            ->orderBy('domain')
-            ->paginate(25);
+        $sites = GuestPreview::paginate(
+            Site::query()
+                ->withCount('pages')
+                ->when(
+                    $this->search !== '',
+                    fn ($query) => $query->where('domain', 'like', '%'.$this->search.'%')
+                )
+                ->orderBy('domain')
+        );
 
         return view('livewire.sites.index', ['sites' => $sites]);
     }