feat(security): add baseline security response headers

next.config.ts

@@ -3,8 +3,36 @@ import createNextIntlPlugin from "next-intl/plugin";
 
 const withNextIntl = createNextIntlPlugin();
 
+// Baseline security headers applied to every response. Deliberately no
+// Content-Security-Policy here: a correct CSP for this app (inline theme
+// script, Google Fonts, Analytics, Turnstile, map tiles) needs to be built
+// and tested against the running app, so it is left as a dedicated follow-up
+// rather than shipped as a guess that could break rendering.
+const securityHeaders = [
+  // Force HTTPS for two years, including subdomains, and allow preload-list
+  // submission.
+  {
+    key: "Strict-Transport-Security",
+    value: "max-age=63072000; includeSubDomains; preload",
+  },
+  // Stop browsers from MIME-sniffing responses away from the declared type.
+  { key: "X-Content-Type-Options", value: "nosniff" },
+  // Disallow framing by other origins (clickjacking protection).
+  { key: "X-Frame-Options", value: "SAMEORIGIN" },
+  // Send only the origin on cross-origin navigations; full URL same-origin.
+  { key: "Referrer-Policy", value: "strict-origin-when-cross-origin" },
+  // Explicitly deny powerful features the site does not use.
+  {
+    key: "Permissions-Policy",
+    value: "camera=(), microphone=(), geolocation=(), browsing-topics=()",
+  },
+];
+
 const nextConfig: NextConfig = {
   output: "standalone",
+  async headers() {
+    return [{ source: "/:path*", headers: securityHeaders }];
+  },
 };
 
 export default withNextIntl(nextConfig);