Use nginx:stable, add nginx config, non-root

Switch the runtime stage to nginx:stable (replacing alpine), remove the default static assets, and copy the built app into /usr/share/nginx/html. Add a custom nginx main config (nginx.main.conf → /etc/nginx/nginx.conf) and keep the default site config. Run the container as the non-root nginx user and expose port 80. These changes ensure the image serves the intended build, uses a stable nginx variant, and improves container security.

nginx.main.conf

@@ -0,0 +1,27 @@
+worker_processes auto;
+pid /tmp/nginx.pid;
+error_log /tmp/error.log warn;
+
+events {
+    worker_connections 1024;
+}
+
+http {
+    include       /etc/nginx/mime.types;
+    default_type  application/octet-stream;
+
+    access_log /tmp/access.log;
+
+    sendfile on;
+    keepalive_timeout 65;
+    server_tokens off;
+
+    # Redefine temp paths to writable tmpfs locations
+    client_body_temp_path /tmp/client_temp;
+    proxy_temp_path       /tmp/proxy_temp;
+    fastcgi_temp_path     /tmp/fastcgi_temp;
+    uwsgi_temp_path       /tmp/uwsgi_temp;
+    scgi_temp_path        /tmp/scgi_temp;
+
+    include /etc/nginx/conf.d/*.conf;
+}