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.

phpunit.xml

@@ -23,8 +23,12 @@
         <env name="BCRYPT_ROUNDS" value="4"/>
         <env name="BROADCAST_CONNECTION" value="null"/>
         <env name="CACHE_STORE" value="array"/>
-        <env name="DB_CONNECTION" value="sqlite"/>
-        <env name="DB_DATABASE" value=":memory:"/>
+        <env name="DB_CONNECTION" value="mysql"/>
+        <env name="DB_HOST" value="192.168.0.155"/>
+        <env name="DB_PORT" value="3306"/>
+        <env name="DB_DATABASE" value="huginn_testing"/>
+        <env name="DB_USERNAME" value="admin"/>
+        <env name="DB_PASSWORD" value="admin"/>
         <env name="DB_URL" value=""/>
         <env name="MAIL_MAILER" value="array"/>
         <env name="QUEUE_CONNECTION" value="sync"/>