docs: align deployment/setup docs with current code

- nginx/docs/PRODUCTION_DEPLOYMENT.md: drop stale htpasswd/Basic-auth model,
  manual server-side deploy step, /var/www/posterg paths and hardcoded IP; describe
  the PHP-layer AdminAuth, automated 📋 Deploying nginx configuration…
xamxam.conf

sent 145 bytes  received 125 bytes  540.00 bytes/sec
total size is 10,012  speedup is 37.08
deploy-server.sh

sent 143 bytes  received 113 bytes  512.00 bytes/sec
total size is 8,519  speedup is 33.28, and what deploy-server.sh
  actually does.
- nginx/docs/QUICK_REFERENCE.md: replace htpasswd user management with AdminAuth
  guidance; fix php8.2->php8.4, log paths, admin rate limit (300r/m), socket path.
- nginx/README.md, nginx/SETUP.md: note 📋 Deploying nginx configuration…
xamxam.conf

sent 145 bytes  received 125 bytes  540.00 bytes/sec
total size is 10,012  speedup is 37.08
deploy-server.sh

sent 143 bytes  received 113 bytes  170.67 bytes/sec
total size is 8,519  speedup is 33.28 automates
  deploy-server.sh (no manual ssh/sudo step).
- docs/deployment.md: correct deploy-code scope (code-only, no --chown), fix the
  /var/log/xamxam provisioning step (deploy-server.sh via deploy-nginx, not
  deploy-code), document the setup-server.sh prerequisite and fresh-box caveat.
- README.md: replace the incomplete manual first-time setup snippet with the
  real setup-server.sh + provision-server flow and a fresh-box caveat.

nginx/SETUP.md

@@ -1,4 +1,4 @@
-# Nginx Setup for Post-ERG
+# Nginx Setup — XAMXAM
 
 Complete setup guide for nginx with security features and password protection.
 
@@ -13,18 +13,15 @@ Complete setup guide for nginx with security features and password protection.
 
 ### 1. Deploy from your local machine
 
+`just deploy-nginx` uploads `nginx/xamxam.conf` and `scripts/deploy-server.sh`, runs the
+script as root on the server (installing the config, fixing permissions, and reloading
+nginx + php-fpm), then cleans up. No manual server-side step is required:
+
 ```bash
 just deploy-nginx
 ```
 
-### 2. Apply on the server
-
-```bash
-ssh xamxam
-sudo bash /tmp/deploy-server.sh
-```
-
-### 3. Set admin password (first time only)
+### 2. Set admin password (first time only)
 
 Visit `/admin/parametres` → Account tab and set the admin password there.