rename posterg → xamxam throughout: nginx conf, scripts, PHP source, docs

nginx/docs/SECURITY_HEADERS.md

@@ -1,4 +1,4 @@
-# Security Headers — nginx/posterg.conf
+# Security Headers — nginx/xamxam.conf
 
 ## Headers in use (main server block — all pages)
 
@@ -18,7 +18,7 @@
 
 These were previously declared in `public/admin/.htaccess` as Apache
 `mod_headers` directives, which nginx silently ignores. They are now
-properly configured in `nginx/posterg.conf`.
+properly configured in `nginx/xamxam.conf`.
 enforced directly; see `HTACCESS_TO_NGINX.md` for the full migration log.
 
 ## Intentionally omitted headers