feat: complete n8n stack setup

Docker Compose stack (n8n, PostgreSQL 16, Redis 7, 1 worker) with:
- nginx local proxy on port 8088, YunoHost TLS termination config
- helper scripts: backup/restore/import/export/update
- .env.example, README with architecture, ops commands, to-do list

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

docs/nginx-local-n8n.conf

@@ -0,0 +1,28 @@
+# Lokale nginx-Konfiguration auf 192.168.179.124
+# Ablegen als: /etc/nginx/sites-available/n8n
+# Aktivieren mit: sudo ln -s /etc/nginx/sites-available/n8n /etc/nginx/sites-enabled/n8n
+# Danach: sudo nginx -t && sudo systemctl reload nginx
+
+server {
+    listen 8088;
+    server_name n8n.linix.de;
+
+    # n8n-Proxy
+    location / {
+        proxy_pass         http://127.0.0.1:5678;
+        proxy_http_version 1.1;
+
+        # WebSocket-Support (n8n Editor + Push-Benachrichtigungen)
+        proxy_set_header   Upgrade    $http_upgrade;
+        proxy_set_header   Connection "upgrade";
+
+        proxy_set_header   Host              $host;
+        proxy_set_header   X-Real-IP         $remote_addr;
+        proxy_set_header   X-Forwarded-For   $proxy_add_x_forwarded_for;
+        proxy_set_header   X-Forwarded-Proto $http_x_forwarded_proto;
+
+        proxy_read_timeout  300s;
+        proxy_send_timeout  300s;
+        client_max_body_size 50m;
+    }
+}