Add Cross-Origin Resource Policy headers for enhanced security

- Introduced Cross-Origin-Resource-Policy header in server.js, nginx.conf, and _headers to restrict resource sharing to same-site origins, improving security against cross-origin attacks.
- Ensured consistent application of Cross-Origin-Opener-Policy and Cross-Origin-Embedder-Policy across server and nginx configurations for better resource management.

public/_headers

@@ -7,6 +7,7 @@
   Permissions-Policy: geolocation=(), camera=(), microphone=(), interest-cohort=()
   Cross-Origin-Opener-Policy: same-origin
   Cross-Origin-Embedder-Policy: credentialless
+  Cross-Origin-Resource-Policy: same-site
   Strict-Transport-Security: max-age=31536000; includeSubDomains; preload
   # Content-Security-Policy starter (enable after auditing inline scripts)
   # Content-Security-Policy: default-src 'self' https://365devnet.eu https://*.365devnet.eu; script-src 'self' 'wasm-unsafe-eval' 'nonce-astro' https://chat.365devnet.eu; style-src 'self' 'unsafe-inline'; img-src 'self' data: https://cdn.pixabay.com https://raw.githubusercontent.com; font-src 'self' data:; connect-src 'self' https://365devnet.eu https://chat.365devnet.eu wss://chat.365devnet.eu; frame-src https://chat.365devnet.eu; frame-ancestors 'none'; base-uri 'self'; form-action 'self'