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>

tests/TestSchema.php

@@ -23,6 +23,7 @@ use DoctrineMigrations\Version20260915000100;
 use DoctrineMigrations\Version20260916000100;
 use DoctrineMigrations\Version20260917000100;
 use DoctrineMigrations\Version20261009000100;
+use DoctrineMigrations\Version20261012000100;
 use Psr\Log\NullLogger;
 
 /**
@@ -57,6 +58,7 @@ final class TestSchema
             Version20260916000100::class,
             Version20260917000100::class,
             Version20261009000100::class,
+            Version20261012000100::class,
         ] as $migration) {
             (new $migration($db, new NullLogger()))->up($schema);
         }