usability fixes

nginx.conf

@@ -12,6 +12,12 @@ http {
         root /usr/share/nginx/html;
         index index.html;
 
+        # Security headers
+        add_header Content-Security-Policy "default-src 'self'; script-src 'self'; style-src 'self' 'unsafe-inline'; img-src 'self' data:; font-src 'self'; connect-src 'self'; object-src 'none'; frame-ancestors 'none'; base-uri 'self'; form-action 'self'" always;
+        add_header Referrer-Policy "strict-origin-when-cross-origin" always;
+        add_header X-Content-Type-Options "nosniff" always;
+        add_header Strict-Transport-Security "max-age=31536000; includeSubDomains; preload" always;
+
         # Gzip compression
         gzip on;
         gzip_types text/plain text/css application/json application/javascript text/xml application/xml text/javascript image/svg+xml;