Bump CACHEBUST to v8 for backend and frontend rebuilds; update Nginx and NostrAuthGuard to handle X-Forwarded-Prefix for NIP-98 compliance

nginx.conf

@@ -41,6 +41,9 @@ server {
         # Trust the outer reverse proxy's X-Forwarded-Proto when present,
         # otherwise fall back to the connection scheme.
         proxy_set_header X-Forwarded-Proto $http_x_forwarded_proto;
+        # Preserve the original /api prefix so NIP-98 URL verification
+        # can reconstruct the URL the client actually signed.
+        proxy_set_header X-Forwarded-Prefix /api;
         proxy_read_timeout 300s;
         proxy_send_timeout 300s;