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/ConsentController.php

@@ -102,7 +102,9 @@ final class ConsentController extends AbstractController
         $target = $request->request->getString('back');
         // Nur ein Pfad dieser Website: `//fremd.example` ist protokollrelativ, und `/\fremd.example`
         // lesen Browser genauso.
-        if ('' === $target || 1 !== preg_match('#^/(?![/\\\\])#', $target)) {
+        // Steuerzeichen und Leerraum ebenfalls nicht: Browser entfernen Tabulator und Zeilenumbruch
+        // aus Adressen, aus `/<Tab>/fremd.example` würde so wieder `//fremd.example`.
+        if ('' === $target || 1 !== preg_match('#^/(?![/\\\\])#', $target) || 1 === preg_match('/[\x00-\x20\x7F\\\\]/', $target)) {
             return '/';
         }