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

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+@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>

FoodsharingSiegen.Server/Dialogs/ConfirmDialog.razor.cs

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+using Blazorise;
+using FoodsharingSiegen.Server.BaseClasses;
+using Microsoft.AspNetCore.Components;
+
+namespace FoodsharingSiegen.Server.Dialogs
+{
+    public partial class ConfirmDialog : FsBase
+    {
+        #region Parameters
+
+        [Parameter]
+        public Func<Task>? OnConfirm { get; set; }
+
+        [Parameter]
+        public string? Message { get; set; }
+
+        #endregion
+
+        #region Public Method ShowAsync
+
+        /// <summary>
+        /// Displays the confirm dialog with the specified title, message, and confirmation action.
+        /// </summary>
+        /// <param name="modalService">The modal service used to display the dialog.</param>
+        /// <param name="title">The title of the confirmation dialog. Defaults to "Bestätigen" if null.</param>
+        /// <param name="message">The message displayed in the confirmation dialog.</param>
+        /// <param name="onConfirm">The action to invoke when the user confirms.</param>
+        /// <returns>A task that represents the asynchronous operation of displaying the dialog.</returns>
+        public static async Task ShowAsync(IModalService modalService, string? title, string? message, Func<Task> onConfirm)
+        {
+            title ??= "Bestätigen";
+
+            var x = new Action<ModalProviderParameterBuilder<ConfirmDialog>>(b =>
+            {
+                b.Add(nameof(OnConfirm), onConfirm);
+                b.Add(nameof(Message), message);
+            });
+
+            var options = new ModalInstanceOptions
+            {
+                Size = ModalSize.Small
+            };
+
+            await modalService.Show(title, x, options);
+        }
+
+        #endregion
+
+        #region Private Method ConfirmClickAsync
+
+        /// <summary>
+        ///     Invokes the confirmation action if it is set.
+        /// </summary>
+        /// <returns>A task that represents the asynchronous operation.</returns>
+        private async Task ConfirmClickAsync()
+        {
+            if (OnConfirm != null) await OnConfirm.Invoke();
+            await ModalService.Hide();
+        }
+
+        #endregion
+    }
+}