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/Discover/Search.php

@@ -3,6 +3,7 @@
 namespace App\Livewire\Discover;
 
 use App\Models\Site;
+use App\Support\GuestPreview;
 use Illuminate\Contracts\View\View;
 use Illuminate\Pagination\LengthAwarePaginator;
 use Livewire\Attributes\Layout;
@@ -67,7 +68,7 @@ class Search extends Component
         if (! $hasQuery) {
             $sites = new LengthAwarePaginator([], 0, 25, 1, ['path' => request()->url()]);
         } else {
-            $sites = Site::query()
+            $sites = GuestPreview::paginate(Site::query()
                 ->when(
                     $keyword !== '',
                     fn ($query) => $query->whereHas(
@@ -98,8 +99,7 @@ class Search extends Component
                     }
                 }])
                 ->orderByDesc('matching_pages_count')
-                ->orderBy('domain')
-                ->paginate(25);
+                ->orderBy('domain'));
         }
 
         return view('livewire.discover.search', ['sites' => $sites, 'hasQuery' => $hasQuery]);