feat: Add Real IP forwarding feature for bare-metal clusters

ベアメタルKubernetesクラスターやLoadBalancer環境において、
PHP側で訪問者の実IPアドレスを取得できる機能を追加。

Changes:
- Add nginx.forwardRealIP configuration in values.yaml
- Implement real_ip_header and set_real_ip_from in Nginx config
- Pass real IP info to PHP-FPM via fastcgi_param
- Add usage example and documentation in README.md
- Create test-real-ip.php for verification
- Update chart version to 8.5.2-a

Features:
- Compatible with existing customConfig.snippet
- Configurable trusted proxy networks
- Supports multi-tier proxy with recursive option
- Default disabled for backward compatibility

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Chart.yaml

@@ -2,6 +2,6 @@ apiVersion: v2
 name: phpfpm
 description: Nginx + PHP-FPM Helm Chart with external DB and optional Selenium support
 type: application
-version: 8.5.2
+version: 8.5.2-a
 appVersion: "8.5.2"
 icon: https://upload.wikimedia.org/wikipedia/commons/thumb/2/27/PHP-logo.svg/330px-PHP-logo.svg.png