Fix bug of preview content.

frontend/src/app/core/rest-services/publications/model/preview.ts

@@ -0,0 +1,7 @@
+export interface PreviewContentRequest {
+    text: string;
+}
+
+export interface PreviewContentResponse {
+    text: string;
+}

frontend/src/app/core/rest-services/publications/publication.rest-service.ts

@@ -2,6 +2,7 @@ import { HttpClient, HttpParams } from '@angular/common/http';
 import { Injectable, inject } from '@angular/core';
 import { last, lastValueFrom } from 'rxjs';
 import { Publication } from './model/publication';
+import { PreviewContentRequest, PreviewContentResponse } from './model/preview';
 
 @Injectable({
   providedIn: 'root'
@@ -31,9 +32,8 @@ export class PublicationRestService {
     return lastValueFrom(this.httpClient.get<Publication[]>('/api/publications', { params }));
   }
 
-  preview(publicationText: string): Promise<string> {
-    const request = { text: publicationText };
-    return lastValueFrom(this.httpClient.post<string>('/api/publications/preview', request));
+  preview(request: PreviewContentRequest): Promise<PreviewContentResponse> {
+    return lastValueFrom(this.httpClient.post<PreviewContentResponse>('/api/publications/preview', request));
   }
 
   delete(publicationId: string): Promise<void> {