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

backend/src/nostr-auth/nostr-auth.guard.ts

@@ -88,9 +88,15 @@ export class NostrAuthGuard extends AuthGuard('nostr') {
       'http';
     const host =
       request.get('host') ?? request.headers.host ?? request.hostname;
+
+    // When behind a reverse proxy that strips a path prefix (e.g. /api),
+    // the proxy should forward X-Forwarded-Prefix so we can reconstruct
+    // the original URL that the client signed in its NIP-98 event.
+    const prefix =
+      (request.headers['x-forwarded-prefix'] as string | undefined) ?? '';
     const path = request.originalUrl ?? request.url ?? '';
 
-    return `${protocolHeader}://${host}${path}`;
+    return `${protocolHeader}://${host}${prefix}${path}`;
   }
 
   private mapErrorToHttpException(error: NostrAuthError) {