Harden KantSites after the security review

- The installer only opens with a per-installation key that install.php
  creates and shows; the key is deleted with the first account.
- Lock files keep .env, the database, backups and logs out of reach when a
  domain points at the project folder instead of public/.
- Linked sections render by their own schema version, so an old section
  cannot carry unfiltered HTML into a newer page.
- Editors no longer move, trash or change areas and post data of published
  pages; a scheduled publication goes live with the revision that was
  scheduled (migration 20261012000100).
- Form stamps are bound to their form, IPv6 senders count per /64, and a
  flood per form or overall stops storing with a visible message.
- The consent redirect rejects control characters, update targets must look
  like 1.2.3, and own CSS cannot reach outside its block.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/EventSubscriber/InstallSubscriber.php

@@ -3,6 +3,7 @@
 namespace App\EventSubscriber;
 
 use App\Ops\Installation;
+use App\Ops\Protection;
 use Symfony\Component\EventDispatcher\EventSubscriberInterface;
 use Symfony\Component\HttpFoundation\RedirectResponse;
 use Symfony\Component\HttpKernel\Event\RequestEvent;
@@ -36,6 +37,8 @@ final class InstallSubscriber implements EventSubscriberInterface
 
     public function onRequest(RequestEvent $event): void
     {
+        // Fehlende Sperrdateien nachtragen (var/, vendor/, Projektstamm) - einmal je Prozess.
+        Protection::ensure($this->projectDir);
         if (!$event->isMainRequest() || is_file($this->projectDir.'/'.self::MARKER)) {
             return;
         }