chore: add Docker deployment behind Caddy

Build the static Next.js export in a reproducible container and expose it
through the existing Caddy network and upstream service name.

nginx.conf

@@ -0,0 +1,41 @@
+server {
+    listen 80;
+    server_name _;
+
+    root /usr/share/nginx/html;
+    index index.html;
+    charset utf-8;
+    server_tokens off;
+
+    gzip on;
+    gzip_vary on;
+    gzip_min_length 1024;
+    gzip_types
+        application/javascript
+        application/json
+        application/xml
+        image/svg+xml
+        text/css
+        text/plain;
+
+    add_header X-Content-Type-Options "nosniff" always;
+    add_header Referrer-Policy "strict-origin-when-cross-origin" always;
+
+    location ^~ /_next/static/ {
+        try_files $uri =404;
+        add_header Cache-Control "public, max-age=31536000, immutable";
+        add_header X-Content-Type-Options "nosniff" always;
+        add_header Referrer-Policy "strict-origin-when-cross-origin" always;
+        access_log off;
+    }
+
+    location / {
+        try_files $uri $uri.html $uri/ =404;
+    }
+
+    error_page 404 /404.html;
+
+    location = /404.html {
+        internal;
+    }
+}