Fix: Remove filtered Include for variants in GetProductsByCategoryAsync

Previous commit (e931f77) only fixed GetAllProductsAsync and GetProductByIdAsync.
This commit fixes GetProductsByCategoryAsync which also had the broken filtered Include syntax.

**Impact**: Variants will now appear when browsing products by category in TeleBot.

🤖 Generated with Claude Code
https://claude.com/claude-code

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

LittleShop/Services/ProductService.cs

@@ -82,8 +82,8 @@ public class ProductService : IProductService
         return await _context.Products
             .Include(p => p.Category)
             .Include(p => p.Photos)
-            .Include(p => p.MultiBuys.Where(v => v.IsActive))
-            .Include(p => p.Variants.Where(v => v.IsActive))
+            .Include(p => p.MultiBuys)
+            .Include(p => p.Variants)
             .Where(p => p.IsActive && p.CategoryId == categoryId)
             .Select(p => new ProductDto
             {