feat: lazy load products in both stores (infinite scroll)

- ProductService: add GetProductsPagedAsync with PaginationState support
- Store/Products: replace load-all with page-by-page lazy loading (12 per page)
- DiscountStore/Products: replace pagination with lazy load (load more button)
- Both stores show 'load more' button + loading indicator + 'all shown' text

src/FrontOffice.Main/Pages/Store/Products.razor

@@ -94,7 +94,7 @@
                 {
                     <MudText Typo="Typo.body2" Class="mud-text-secondary">
                         <MudIcon Icon="@Icons.Material.Filled.Inventory2" Size="Size.Small" Class="me-1"/>
-                        @(_products.Count) محصول
+                        @(_totalCount) محصول
                     </MudText>
                 }
             </MudItem>
@@ -159,5 +159,30 @@
                 </MudItem>
             }
         </MudGrid>
+
+        @* Lazy Load — بارگذاری بیشتر *@
+        @if (_loadingMore)
+        {
+            <MudStack AlignItems="AlignItems.Center" Class="py-4">
+                <MudProgressCircular Color="Color.Primary" Size="Size.Small" Indeterminate="true"/>
+                <MudText Typo="Typo.caption" Class="mud-text-secondary">بارگذاری بیشتر...</MudText>
+            </MudStack>
+        }
+        else if (_hasMore)
+        {
+            <div class="d-flex justify-center py-4">
+                <MudButton Variant="Variant.Outlined" Color="Color.Primary"
+                           StartIcon="@Icons.Material.Filled.ExpandMore"
+                           OnClick="LoadMore">
+                    نمایش محصولات بیشتر
+                </MudButton>
+            </div>
+        }
+        else if (_products.Count > 0)
+        {
+            <MudText Typo="Typo.caption" Align="Align.Center" Class="py-4 mud-text-secondary">
+                همه @(_products.Count) محصول نمایش داده شد
+            </MudText>
+        }
     }
 </MudContainer>

src/FrontOffice.Main/Pages/Store/Products.razor.cs

@@ -24,6 +24,11 @@ public partial class Products : ComponentBase, IDisposable
 
     private string _query = string.Empty;
     private bool _loading;
+    private bool _loadingMore;
+    private bool _hasMore = true;
+    private int _currentPage = 1;
+    private int _totalCount;
+    private const int PageSize = 12;
     private List<Product> _products = new();
     private long? _activeCategoryId;
     private string? _activeCategoryTitle;
@@ -36,7 +41,7 @@ public partial class Products : ComponentBase, IDisposable
         await Cart.EnsureInitializedAsync();
         Cart.OnChange += StateHasChanged;
         Navigation.LocationChanged += HandleLocationChanged;
-        await Load();
+        await LoadInitial();
     }
 
     protected override async Task OnAfterRenderAsync(bool firstRender)
@@ -49,18 +54,40 @@ public partial class Products : ComponentBase, IDisposable
         await base.OnAfterRenderAsync(firstRender);
     }
 
-    private async Task Load()
+    private async Task LoadInitial()
     {
         _loading = true;
+        _currentPage = 1;
+        _products.Clear();
         UpdateCategoryFilterFromUri();
         var sortBy = GetSortByValue();
-        _products = await ProductService.GetProductsAsync(_query, _activeCategoryId, sortBy);
+        var result = await ProductService.GetProductsPagedAsync(_query, _activeCategoryId, sortBy, _currentPage, PageSize);
+        _products = result.Products;
+        _hasMore = result.HasNext;
+        _totalCount = result.TotalCount;
         _activeCategoryTitle = _activeCategoryId is { } categoryId
             ? (await CategoryService.GetByIdAsync(categoryId))?.Title
             : null;
         _loading = false;
     }
 
+    private async Task LoadMore()
+    {
+        if (_loadingMore || !_hasMore) return;
+        
+        _loadingMore = true;
+        StateHasChanged();
+        
+        _currentPage++;
+        var sortBy = GetSortByValue();
+        var result = await ProductService.GetProductsPagedAsync(_query, _activeCategoryId, sortBy, _currentPage, PageSize);
+        _products.AddRange(result.Products);
+        _hasMore = result.HasNext;
+        
+        _loadingMore = false;
+        StateHasChanged();
+    }
+
     private string GetSortByValue()
     {
         return _sortOption switch
@@ -75,12 +102,12 @@ public partial class Products : ComponentBase, IDisposable
 
     private async Task OnSortChanged()
     {
-        await Load();
+        await LoadInitial();
     }
 
     private async Task OnQueryChanged(KeyboardEventArgs _)
     {
-        await Load();
+        await LoadInitial();
     }
 
     private async Task AddToCart(Product p)
@@ -98,7 +125,7 @@ public partial class Products : ComponentBase, IDisposable
 
     private void HandleLocationChanged(object? sender, LocationChangedEventArgs args)
     {
-        _ = InvokeAsync(Load);
+        _ = InvokeAsync(LoadInitial);
     }
 
     private void UpdateCategoryFilterFromUri()