feat: add monitoring dashboard under /monitor/

Status page and JSON API read from private/data; root index.php stays a placeholder. Mark todo 06 done.

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

public/monitor/status.php

@@ -0,0 +1,18 @@
+<?php
+
+declare(strict_types=1);
+
+$root = dirname(dirname(__DIR__));
+$configDir = is_dir($root . '/private/config')
+    ? $root . '/private/config'
+    : $root . '/config';
+
+require_once $configDir . '/status-view.php';
+
+$status = formatPublicStatus(loadStatusSnapshot());
+
+header('Content-Type: application/json; charset=utf-8');
+header('X-Robots-Tag: noindex');
+header('Cache-Control: no-store');
+
+echo json_encode($status, JSON_PRETTY_PRINT | JSON_UNESCAPED_SLASHES) . "\n";