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/Utilities/ProductService.cs

@@ -26,6 +26,13 @@ public record Product(
         = [];
 }
 
+public record ProductListResult(
+    List<Product> Products,
+    int TotalCount,
+    int TotalPages,
+    int CurrentPage,
+    bool HasNext);
+
 public record ProductGalleryImage(
     long ProductGalleryId,
     long ProductImageId,
@@ -59,11 +66,24 @@ public class ProductService
     }
 
     public async Task<List<Product>> GetProductsAsync(string? query = null, long? categoryId = null, string? sortBy = null)
+    {
+        var result = await GetProductsPagedAsync(query: query, categoryId: categoryId, sortBy: sortBy, page: 1, pageSize: 500);
+        return result.Products;
+    }
+
+    public async Task<ProductListResult> GetProductsPagedAsync(
+        string? query = null, long? categoryId = null, string? sortBy = null,
+        int page = 1, int pageSize = 12)
     {
         try
         {
             var request = new GetAllProductsByFilterRequest
             {
+                PaginationState = new CMSMicroservice.Protobuf.Protos.PaginationState
+                {
+                    PageNumber = page,
+                    PageSize = pageSize
+                },
                 Filter = new GetAllProductsByFilterFilter
                 {
                     Title = query ?? string.Empty,
@@ -84,7 +104,12 @@ public class ProductService
             }
 
             var resp = await _client.GetAllProductsByFilterAsync(request);
-            return MapAndCache(resp.Models);
+            var products = MapAndCache(resp.Models);
+            var totalCount = (int)(resp.MetaData?.TotalCount ?? 0);
+            var totalPages = (int)(resp.MetaData?.TotalPage ?? 0);
+            var hasNext = resp.MetaData?.HasNext ?? false;
+
+            return new ProductListResult(products, totalCount, totalPages, page, hasNext);
         }
         catch
         {
@@ -97,7 +122,8 @@ public class ProductService
                     p.Description.Contains(q, StringComparison.OrdinalIgnoreCase));
             }
 
-            return list.OrderBy(p => p.Id).ToList();
+            var all = list.OrderBy(p => p.Id).ToList();
+            return new ProductListResult(all, all.Count, 1, 1, false);
         }
     }