feat: add Docker setup for documentation site

- Dockerfile.docs for building docs container
- nginx.conf for serving static Starlight site
- docker-compose.yml updated with docs service (--profile docs)
- Updated docs installation/deployment pages

docs/nginx.conf

@@ -0,0 +1,28 @@
+server {
+    listen 80;
+    server_name _;
+
+    root /usr/share/nginx/html;
+    index index.html;
+
+    # Starlight static site
+    location / {
+        try_files $uri $uri/ $uri.html =404;
+    }
+
+    # SPA fallback for client-side routing
+    location ~ ^/[^.]+$ {
+        try_files $uri $uri.html =404;
+    }
+
+    # Cache static assets
+    location ~* \.(js|css|png|jpg|jpeg|gif|ico|svg|woff|woff2)$ {
+        expires 1y;
+        add_header Cache-Control "public, immutable";
+    }
+
+    # Security headers
+    add_header X-Frame-Options "SAMEORIGIN" always;
+    add_header X-Content-Type-Options "nosniff" always;
+    add_header X-XSS-Protection "1; mode=block" always;
+}