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()

.gitignore

@@ -21,6 +21,10 @@ Thumbs.db
 *.tmp
 *.temp
 
+# Local configuration & credentials
+config.json
+admin/config/admin.json
+
 # No content
 content/
 !content/.gitkeep