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/Support/GuestPreview.php

@@ -0,0 +1,33 @@
+<?php
+
+namespace App\Support;
+
+use Illuminate\Contracts\Pagination\LengthAwarePaginator;
+use Illuminate\Database\Eloquent\Builder;
+use Illuminate\Database\Eloquent\Relations\Relation;
+
+/**
+ * Caps a listing to a small preview for unauthenticated visitors — always page 1,
+ * always a short page, regardless of what page/perPage the request asks for — while
+ * authenticated users get the real, full pagination. total() still reflects the true
+ * match count either way, so guests see "N results, sign in to see all" rather than a
+ * silently truncated list.
+ */
+class GuestPreview
+{
+    public const LIMIT = 5;
+
+    public static function paginate(Builder|Relation $query, int $fullPerPage = 25, string $pageName = 'page'): LengthAwarePaginator
+    {
+        if (self::isLimited()) {
+            return $query->paginate(self::LIMIT, ['*'], $pageName, 1);
+        }
+
+        return $query->paginate($fullPerPage, ['*'], $pageName);
+    }
+
+    public static function isLimited(): bool
+    {
+        return ! auth()->check();
+    }
+}