feat: Extract Developer Portal as standalone Next.js app on port 3006

SDK customers can now access the documentation publicly without login.
The portal runs independently from admin-v2 on https://macmini:3006/.

- New developer-portal/ app with 26 pages, 2 components
- Docker service + nginx SSL reverse proxy on port 3006
- All /developers/* routes remapped to /* in the new app
- admin-v2 developer pages remain unchanged

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

nginx/conf.d/default.conf

@@ -317,6 +317,33 @@ server {
     }
 }
 
+# HTTPS - Developer Portal on port 3006
+# Oeffentliches SDK-Dokumentationsportal (kein Auth)
+server {
+    listen 3006 ssl;
+    http2 on;
+    server_name macmini localhost;
+
+    ssl_certificate /etc/nginx/certs/macmini.crt;
+    ssl_certificate_key /etc/nginx/certs/macmini.key;
+
+    ssl_protocols TLSv1.2 TLSv1.3;
+    ssl_ciphers ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256;
+    ssl_prefer_server_ciphers off;
+
+    location / {
+        set $upstream_devportal developer-portal:3000;
+        proxy_pass http://$upstream_devportal;
+        proxy_http_version 1.1;
+        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 https;
+    }
+}
+
 # HTTPS - AI Compliance SDK on port 8093
 # Multi-Tenant RBAC, LLM Gateway, Audit Trail
 server {