Refactor interaction and user deletion logic

Consolidated repeated methods for interaction/user deletion into reusable components to improve maintainability. Introduced a `ConfirmDialog` for consistent confirmation UI and streamlined associated logic across pages. Removed redundant methods and enhanced admin-specific page security checks.

FoodsharingSiegen.Server/Dialogs/ConfirmDialog.razor

@@ -0,0 +1,10 @@
+@inherits FsBase
+
+<div class="mt-1 mb-3">
+  @Message
+</div>
+
+<div class="d-flex justify-content-end">
+  <Button Color="Color.Secondary" Clicked="@ModalService.Hide">Abbrechen</Button>
+  <Button Color="Color.Primary" Clicked="@ConfirmClickAsync" Class="ml-2">OK</Button>
+</div>