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/movie-poster/movie-poster.component.html

@@ -1,5 +1,10 @@
 <div class="w-64 mx-auto my-2">
-  <img [src]="movie().image" alt="Movie Poster" class="w-full h-auto shadow-md">
+  <img
+    [src]="movie().image && movie().image !== 'N/A' ? movie().image : 'assets/poster_placeholder.png'"
+    alt="Movie Poster"
+    class="w-full h-auto shadow-md rounded-md"
+    (error)="onPosterError($event)"
+  >
 </div>
 <div class="flex gap-1 justify-between">
   <app-movie-rating [rating]="movie().rating"></app-movie-rating>