feat: external HTTPS monitoring pull via monitor.php

Add cron-ready pull checks for critical URLs with SSL expiry warnings,
retry-before-alert, JSON results in private/data, email alerts, and a
90-day target-list review reminder.

Co-authored-by: Cursor <cursoragent@cursor.com>

config/targets.php

@@ -0,0 +1,23 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * External HTTPS monitoring targets.
+ * After manual infra review: bump _meta.last_reviewed_at and deploy.
+ */
+
+return [
+    '_meta' => [
+        'last_reviewed_at' => '2026-06-12',
+    ],
+    'targets' => [
+        ['name' => 'schwenk.online', 'url' => 'https://schwenk.online', 'expect' => 200],
+        ['name' => 'gitea', 'url' => 'https://gitea.schwenk.online', 'expect' => 200],
+        ['name' => 'pics', 'url' => 'https://pics.schwenk.online', 'expect' => 200],
+        ['name' => 'medis', 'url' => 'https://medis.schwenk.online', 'expect' => 200],
+        ['name' => 'portainer', 'url' => 'https://portainer.schwenk.online', 'expect' => [200, 401]],
+        ['name' => 'score.bsc-gp.de', 'url' => 'https://score.bsc-gp.de', 'expect' => 200],
+        ['name' => 'vfb.red', 'url' => 'https://vfb.red', 'expect' => 200],
+    ],
+];