Real JSON null for empty product feature; SSR warm-cache button and CLI

Ticket 0068-FE: ProductFeatureJsonRenderer returned json_encode(null), which headless passes on as the STRING null (it only decodes object/array-looking strings) and crashed the front end. It now returns an empty string and the TypoScript field sets ifEmptyReturnNull = 1, giving a real JSON null. No other renderer used the pattern. Ticket 0066-FE: SsrPurgeService::warm() posts to the node /__warm endpoint (derived from SSR_PURGE_ENDPOINT, same secret), exposed as a Warm cache button with confirmation in the VITEC SSR module, a Cache warming progress row fed by /__health, and the CLI vitec:ssr-warm [paths]. Warm runs are deliberately not written to the purge log. Verified: two-path run 2/2 done, affected page delivers productfeature null.

Co-Authored-By: Claude Fable 5.2 <noreply@anthropic.com>

packages/vitec/Classes/Command/SsrWarmCommand.php

@@ -0,0 +1,36 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Evomedien\Vitec\Command;
+
+use Evomedien\Vitec\Service\SsrPurgeService;
+use Symfony\Component\Console\Attribute\AsCommand;
+use Symfony\Component\Console\Command\Command;
+use Symfony\Component\Console\Input\InputArgument;
+use Symfony\Component\Console\Input\InputInterface;
+use Symfony\Component\Console\Output\OutputInterface;
+
+#[AsCommand(
+    name: 'vitec:ssr-warm',
+    description: 'Start a background warm run on the SSR node (all sitemap pages, or the given paths)',
+)]
+final class SsrWarmCommand extends Command
+{
+    public function __construct(private readonly SsrPurgeService $purgeService)
+    {
+        parent::__construct();
+    }
+
+    protected function configure(): void
+    {
+        $this->addArgument('paths', InputArgument::IS_ARRAY, 'Paths to warm; none = every page of sitemap.xml');
+    }
+
+    protected function execute(InputInterface $input, OutputInterface $output): int
+    {
+        $result = $this->purgeService->warm((array)$input->getArgument('paths'));
+        $output->writeln(($result['success'] ? '<info>OK</info> ' : '<error>FAILED</error> ') . $result['message']);
+        return $result['success'] ? Command::SUCCESS : Command::FAILURE;
+    }
+}