Add IMDb movie importer feature and unify header

Introduces a new movie importer feature allowing admins to search and import movies from IMDb, including new components for search, result display, and error handling. Replaces the schedule header with a reusable menu header component. Updates routing, navigation, and HTTP service to support the new importer. Adds a poster placeholder image and improves poster error handling.

src/app/schedule/schedule.component.html

@@ -1,4 +1,4 @@
-<app-schedule-header (movieSearchResult)="movieSearchResult = $event"></app-schedule-header>
+<app-menu-header title="Programmübersicht" icon="event" [searchBar]="true" (movieSearchResult)="movieSearchResult = $event"></app-menu-header>
 
 <mat-tab-group mat-stretch-tabs>
   @for (dateInfo of dates; track dateInfo.date; let i = $index) {

src/app/schedule/schedule.component.ts

@@ -4,7 +4,7 @@ import { Vorstellung } from '@infinimotion/model-frontend';
 import { Performance } from '../model/performance.model';
 import { MovieGroup } from '../model/movie-group.model';
 import { LoadingService } from '../loading.service';
-import { catchError, map, of, tap } from 'rxjs';
+import { catchError, of, tap } from 'rxjs';
 
 @Component({
   selector: 'app-schedule',
@@ -61,8 +61,7 @@ export class ScheduleComponent implements OnInit {
   loadPerformances(bookableDays: number) {
     this.loading.show();
     const filter = this.generateDateFilter(bookableDays);
-    this.http.getPerformaceByFilter(filter).pipe(
-      map(data => Array.isArray(data) ? data : [data]),
+    this.http.getPerformacesByFilter(filter).pipe(
       tap(performaces => {
         this.performaces = performaces;
         this.assignPerformancesToDates();