fix(security): add CSRF protection to all POST endpoints + contract tests (B2)

CSRF guards added to 16 admin pages that previously accepted POST requests
without token verification (GR-SEC-001): departments, permissions, roles,
settings, tenants, users (create/edit/bulk/tokens), and lang switch.

New contract tests:
- PostEndpointCsrfContractTest: scans all pages/ for POST handlers and
  verifies checkCsrfToken is present (API/data endpoints exempt).
- DatabaseUpdatesContractTest: validates db/updates/ scripts follow naming
  convention and use idempotent SQL patterns (GR-CORE-010).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

pages/admin/users/bulk($action).php

@@ -4,11 +4,17 @@ use MintyPHP\Http\SessionStoreInterface;
 use MintyPHP\Router;
 use MintyPHP\Service\Access\UserAuthorizationPolicy;
 use MintyPHP\Service\User\UserAccessTemplateService;
+use MintyPHP\Session;
 use MintyPHP\Support\Guard;
 
 $session = app(SessionStoreInterface::class)->all();
 Guard::requireLogin();
 
+if (!Session::checkCsrfToken()) {
+    Router::json(['ok' => false, 'error' => 'csrf_expired']);
+    return;
+}
+
 $action = strtolower(trim((string) ($action ?? '')));
 $allowedActions = ['activate', 'deactivate', 'delete', 'send-access'];
 if (!in_array($action, $allowedActions, true)) {