Add system update feature, git-ignore local configs, and fix homepage request logging

- Exclude config.json and admin.json in .gitignore so live settings/passwords are never overwritten by git
- Auto-generate config.json and admin.json with defaults if missing
- Add config.json.example and admin.json.example reference templates
- Add System Update page (/admin/update) in Admin Console to pull updates via Git with 1 click
- Log effective page name in index.php instead of literal 'auto'
- Add extra HAProxy/PFSense proxy headers to RequestLogger::getClientIp()

public/index.php

@@ -111,7 +111,7 @@ if (!str_starts_with($path, '/-media/') && !str_starts_with($path, '/-assets/'))
     $requestLogFile = dirname(__DIR__) . '/admin/storage/logs/requests.log';
     $logger = new RequestLogger($requestLogFile);
     $logger->log(
-        $_GET['page'] ?? $config['default_page'] ?? 'index',
+        $_GET['page'] ?? $cms->getEffectiveDefaultPage(),
         RequestLogger::getClientIp(),
         $_SERVER['HTTP_USER_AGENT'] ?? '',
         $_SERVER['HTTP_REFERER'] ?? '',