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/App.razor

@@ -1,4 +1,4 @@
-<Blazorise.ThemeProvider Theme="@theme">
+<Blazorise.ThemeProvider Theme="@_theme">
     <Router AppAssembly="@typeof(App).Assembly">
         <Found Context="routeData">
             <AuthorizeRouteView RouteData="@routeData" DefaultLayout="@typeof(DefaultLayout)">
@@ -13,15 +13,14 @@
         </NotFound>
     </Router>
 
-    <MessageProvider />
     <ModalProvider Centered="true" />
 </Blazorise.ThemeProvider>
 
 
 @code{
-    private Theme theme = new()
+    private readonly Theme _theme = new()
     {
-        ColorOptions = new ThemeColorOptions
+        ColorOptions = new()
         {
             Primary = "#64ae24",
             Secondary = "#533a20",