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/Controller/FormController.php

@@ -46,12 +46,12 @@ final class FormController extends AbstractController
         if (null === $form || null === $page) {
             throw $this->createNotFoundException('Formular oder Seite nicht gefunden.');
         }
-        $senderHash = hash_hmac('sha256', (string) $request->getClientIp(), $this->secret);
+        $senderHash = FormRepository::senderKey($request->getClientIp(), $this->secret);
 
         // Three quiet checks before the real validation. A caught bot is answered like a success
         // so it learns nothing, but nothing is stored and nothing is sent.
         $silentlyDropped = '' !== trim($request->request->getString('website'))
-            || !$this->timingIsPlausible($request)
+            || !$this->timingIsPlausible($request, $slug)
             || $this->forms->rateLimited($senderHash)
             // Die vierte, freiwillige Pruefung. Sie antwortet wie die drei anderen still mit
             // Erfolg: ein Absender, der erfaehrt, woran er gescheitert ist, versucht es gezielt
@@ -72,6 +72,11 @@ final class FormController extends AbstractController
             // Re-render the page the form sits on, with the entered values and the messages.
             return $this->renderPage($request, $page, $form, $checked, null === $language ? null : ($page['path'] === $this->settings->homePath() ? $language : $language.'/'.$translatedPath));
         }
+        // Kommt gerade für dieses Formular oder insgesamt zu viel an, wird nichts mehr gespeichert -
+        // aber sichtbar, nicht still: ein echter Besucher soll wissen, dass er anrufen muss.
+        if (!$silentlyDropped && $this->forms->flooded($form['id'])) {
+            return $this->renderPage($request, $page, $form, ['errors' => ['_form' => 'Gerade gehen sehr viele Anfragen ein. Bitte versuchen Sie es später erneut oder melden Sie sich telefonisch.'], 'values' => $checked['values']], null === $language ? null : ($page['path'] === $this->settings->homePath() ? $language : $language.'/'.$translatedPath));
+        }
         if (!$silentlyDropped) {
             $submission = $this->forms->store($form['id'], $checked['values'], $checked['consent'], $senderHash);
             if ($this->deliver($form, $checked['values'])) {
@@ -86,10 +91,10 @@ final class FormController extends AbstractController
     }
 
     /** The signed timestamp makes the age of the form checkable without storing anything. */
-    private function timingIsPlausible(Request $request): bool
+    private function timingIsPlausible(Request $request, string $slug): bool
     {
         $issued = $request->request->getInt('issued');
-        if (!hash_equals(hash_hmac('sha256', (string) $issued, $this->secret), $request->request->getString('issuedSignature'))) {
+        if (!hash_equals(FormRepository::stamp($slug, $issued, $this->secret), $request->request->getString('issuedSignature'))) {
             return false;
         }
         $age = time() - $issued;