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/navbar/navbar.component.ts

@@ -13,6 +13,7 @@ export class NavbarComponent {
 
   navItems:{label:string, path:string}[] = [
     {label: 'Programm', path: '/schedule'},
+    {label: 'Film importieren', path: '/admin/movie-importer'},
     {label: 'Kinosaal-test', path: '/theater-overlay'},
   ]
 }