feat(G5): add PendingMembershipsWidget

- new PendingMembershipsWidget.razor shows pending membership count
- only visible to club admins/super admins
- integrated into Dashboard.razor
- click navigates to admin users page

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/Koogle.Web/Components/Pages/Dashboard.razor

@@ -4,6 +4,7 @@
 @using Koogle.Application.DTOs
 @using Koogle.Application.Interfaces
 @using Koogle.Domain.Enums
+@using Koogle.Web.Components.Shared
 @using Microsoft.AspNetCore.Authorization
 
 @inject IDashboardService DashboardService
@@ -102,6 +103,11 @@ else if (_dashboard is not null)
             </MudCard>
         </MudItem>
 
+        <!-- Pending Memberships Widget (Admin only) -->
+        <MudItem xs="12">
+            <PendingMembershipsWidget />
+        </MudItem>
+
         <!-- Top Penalty Recipients -->
         <MudItem xs="12" md="6">
             <MudCard Elevation="2">

src/Koogle.Web/Components/Shared/PendingMembershipsWidget.razor

@@ -0,0 +1,90 @@
+@using Fluxor
+@using Koogle.Application.DTOs
+@using Koogle.Application.Interfaces
+@using Koogle.Web.Store.AuthState
+
+@inherits Fluxor.Blazor.Web.Components.FluxorComponent
+
+@inject IUserService UserService
+@inject IState<AuthState> AuthState
+@inject NavigationManager NavigationManager
+@inject ISnackbar Snackbar
+
+@if (_isLoading)
+{
+    <MudProgressLinear Indeterminate="true" Color="Color.Primary" />
+}
+else if (_pendingCount > 0)
+{
+    <MudCard Elevation="2" Style="cursor: pointer" @onclick="NavigateToUsers">
+        <MudCardContent Class="d-flex flex-column align-center">
+            <MudBadge Content="@_pendingCount" Color="Color.Error" Overlap="true">
+                <MudIcon Icon="@Icons.Material.Filled.PersonAdd" Size="Size.Large" Color="Color.Warning" />
+            </MudBadge>
+            <MudText Typo="Typo.h6" Class="mt-2">Offene Beitrittsanträge</MudText>
+            <MudText Typo="Typo.body2" Color="Color.Secondary">
+                @(_pendingCount == 1 ? "1 Antrag wartet auf Freigabe" : $"{_pendingCount} Anträge warten auf Freigabe")
+            </MudText>
+        </MudCardContent>
+    </MudCard>
+}
+
+@code {
+    private int _pendingCount;
+    private bool _isLoading = true;
+
+    protected override async Task OnInitializedAsync()
+    {
+        await base.OnInitializedAsync();
+        await LoadPendingCountAsync();
+    }
+
+    private async Task LoadPendingCountAsync()
+    {
+        try
+        {
+            _isLoading = true;
+            var state = AuthState.Value;
+            var clubId = state.CurrentClub?.ClubId ?? Guid.Empty;
+
+            if (clubId == Guid.Empty)
+            {
+                _pendingCount = 0;
+                return;
+            }
+
+            // Only load for club admins or super admins
+            if (!state.IsClubAdmin && !state.IsSuperAdmin)
+            {
+                _pendingCount = 0;
+                return;
+            }
+
+            var pending = await UserService.GetPendingMembershipsAsync(clubId);
+            _pendingCount = pending.Count;
+        }
+        catch (Exception ex)
+        {
+            Snackbar.Add($"Fehler beim Laden der Anträge: {ex.Message}", Severity.Error);
+            _pendingCount = 0;
+        }
+        finally
+        {
+            _isLoading = false;
+        }
+    }
+
+    /// <summary>
+    /// Reloads pending membership count.
+    /// </summary>
+    public async Task RefreshAsync()
+    {
+        await LoadPendingCountAsync();
+        StateHasChanged();
+    }
+
+    private void NavigateToUsers()
+    {
+        NavigationManager.NavigateTo("/admin/users");
+    }
+}