Add LittleShop.Client SDK library with complete API wrapper

Features:
- Complete .NET client SDK for LittleShop API
- JWT authentication with automatic token management
- Catalog service for products and categories
- Order service with payment creation
- Retry policies using Polly for resilience
- Error handling middleware
- Dependency injection support
- Comprehensive documentation and examples

SDK Components:
- Authentication service with token refresh
- Strongly-typed models for all API responses
- HTTP handlers for retry and error handling
- Extension methods for easy DI registration
- Example console application demonstrating usage

Test Updates:
- Fixed test compilation errors
- Updated test data builders for new models
- Corrected service constructor dependencies
- Fixed enum value changes (PaymentStatus, OrderStatus)

Documentation:
- Complete project README with features and usage
- Client SDK README with detailed examples
- API endpoint documentation
- Security considerations
- Deployment guidelines

Generated with Claude Code

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

LittleShop.Tests/TestUtilities/TestDataBuilder.cs

@@ -78,12 +78,9 @@ public static class TestDataBuilder
         {
             Id = Guid.NewGuid(),
             Username = user,
-            Email = $"{user}@test.com",
             PasswordHash = "hashed-password",
-            Role = role,
             IsActive = true,
-            CreatedAt = DateTime.UtcNow,
-            UpdatedAt = DateTime.UtcNow
+            CreatedAt = DateTime.UtcNow
         };
     }
 
@@ -94,12 +91,11 @@ public static class TestDataBuilder
             Id = Guid.NewGuid(),
             OrderId = orderId,
             Currency = currency,
-            Amount = 0.0025m,
-            CryptoAddress = $"bc1q{Guid.NewGuid().ToString().Replace("-", "").Substring(0, 39)}",
+            RequiredAmount = 0.0025m,
+            WalletAddress = $"bc1q{Guid.NewGuid().ToString().Replace("-", "").Substring(0, 39)}",
             Status = status,
-            ExchangeRate = 40000.00m,
             CreatedAt = DateTime.UtcNow,
-            UpdatedAt = DateTime.UtcNow
+            ExpiresAt = DateTime.UtcNow.AddHours(1)
         };
     }
 
@@ -161,15 +157,17 @@ public static class TestDataBuilder
         };
     }
 
-    public static ProductPhoto CreateProductPhoto(Guid productId, int displayOrder = 1)
+    public static ProductPhoto CreateProductPhoto(Guid productId, int sortOrder = 1)
     {
+        var fileName = $"{Guid.NewGuid()}.jpg";
         return new ProductPhoto
         {
             Id = Guid.NewGuid(),
             ProductId = productId,
-            PhotoUrl = $"/uploads/products/{Guid.NewGuid()}.jpg",
+            FileName = fileName,
+            FilePath = $"/uploads/products/{fileName}",
             AltText = "Test product photo",
-            DisplayOrder = displayOrder,
+            SortOrder = sortOrder,
             CreatedAt = DateTime.UtcNow
         };
     }