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.Client/Models/Order.cs

@@ -0,0 +1,51 @@
+namespace LittleShop.Client.Models;
+
+public class Order
+{
+    public Guid Id { get; set; }
+    public string IdentityReference { get; set; } = string.Empty;
+    public string Status { get; set; } = string.Empty;
+    public decimal TotalAmount { get; set; }
+    public string Currency { get; set; } = string.Empty;
+    public string ShippingName { get; set; } = string.Empty;
+    public string ShippingAddress { get; set; } = string.Empty;
+    public string ShippingCity { get; set; } = string.Empty;
+    public string ShippingPostCode { get; set; } = string.Empty;
+    public string ShippingCountry { get; set; } = string.Empty;
+    public string? Notes { get; set; }
+    public string? TrackingNumber { get; set; }
+    public List<OrderItem> Items { get; set; } = new();
+    public List<CryptoPayment> Payments { get; set; } = new();
+    public DateTime CreatedAt { get; set; }
+    public DateTime UpdatedAt { get; set; }
+    public DateTime? PaidAt { get; set; }
+    public DateTime? ShippedAt { get; set; }
+}
+
+public class OrderItem
+{
+    public Guid Id { get; set; }
+    public Guid ProductId { get; set; }
+    public string? ProductName { get; set; }
+    public int Quantity { get; set; }
+    public decimal UnitPrice { get; set; }
+    public decimal TotalPrice { get; set; }
+}
+
+public class CreateOrderRequest
+{
+    public string IdentityReference { get; set; } = string.Empty;
+    public string ShippingName { get; set; } = string.Empty;
+    public string ShippingAddress { get; set; } = string.Empty;
+    public string ShippingCity { get; set; } = string.Empty;
+    public string ShippingPostCode { get; set; } = string.Empty;
+    public string ShippingCountry { get; set; } = "United Kingdom";
+    public string? Notes { get; set; }
+    public List<CreateOrderItem> Items { get; set; } = new();
+}
+
+public class CreateOrderItem
+{
+    public Guid ProductId { get; set; }
+    public int Quantity { get; set; }
+}