security: comprehensive hardening across frontend, backend, and infrastructure

- Disable production source maps and hide nginx version
- Reduce JSON body limit from 10gb to 50mb (uploads use multer, not JSON)
- Strip database info and error details from health endpoint
- Mask reCAPTCHA secret key in admin settings API responses
- Whitelist sort/order query parameters in events and photos endpoints
- Stop reflecting arbitrary origins in static file CORS headers
- Align nginx security headers with backend Helmet CSP, remove deprecated X-XSS-Protection
- Strip EXIF metadata from generated thumbnails and hero images
- Bind postgres/redis dev ports to localhost in docker-compose configs
- Add safeExec utility (spawn with shell:false) to prevent command injection
- Convert all exec/execAsync calls in backup, restore, and database backup
  services to use safe spawn-based helpers

frontend/nginx.conf

@@ -1,6 +1,7 @@
 server {
     listen 80;
     server_name localhost;
+    server_tokens off;
     root /usr/share/nginx/html;
     index index.html;
 
@@ -21,9 +22,9 @@ server {
     # 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;
-    add_header Referrer-Policy "no-referrer-when-downgrade" always;
-    add_header Content-Security-Policy "default-src 'self' http: https: data: blob: 'unsafe-inline' 'unsafe-eval'" always;
+    add_header Referrer-Policy "strict-origin-when-cross-origin" always;
+    add_header Permissions-Policy "camera=(), microphone=(), geolocation=(), payment=()" always;
+    add_header Content-Security-Policy "default-src 'self'; script-src 'self' https://www.google.com https://www.gstatic.com; style-src 'self' 'unsafe-inline' https:; img-src 'self' data: https: blob:; connect-src 'self' https://www.google.com https://www.gstatic.com; font-src 'self' https: data:; object-src 'none'; media-src 'self'; frame-src 'self' https://www.google.com" always;
 
     # Health check endpoint
     location /health {