Document enum property support and serialization options

[dguisinger]

Once enum support is implemented #125 , documentation needs to be updated to explain enum usage and the Format option for controlling storage representation.

Sections to Update

docs/core-features/EntityDefinition.md — Add enum property examples to the supported types section
.kiro/steering/fluentdynamodb.md — Add enum examples to the Entity Definition section
docs/CodeExamples.md — Add practical enum usage examples
README.md — Mention enum support in the features list if not already present

Content to Document

public enum OrderStatus { Pending, Processing, Shipped, Delivered, Cancelled }

[DynamoDbTable("Orders")]
public partial class Order
{
    [PartitionKey]
    [DynamoDbAttribute("pk")]
    public string Pk { get; set; } = string.Empty;

    // Default: stores as string name → { "S": "Shipped" }
    [DynamoDbAttribute("status")]
    public OrderStatus Status { get; set; }

    // With Format = "D": stores as integer → { "N": "2" }
    [DynamoDbAttribute("statusCode", Format = "D")]
    public OrderStatus StatusCode { get; set; }

    // Nullable enum
    [DynamoDbAttribute("previousStatus")]
    public OrderStatus? PreviousStatus { get; set; }
}

Key Points to Cover

• Default behavior: stored as string name in S attribute
• Format = "D": stored as numeric value in N attribute
• Nullable enum support
• Enums in collections (List, HashSet)
• Interop note: AWS SDK's Object Persistence Model stores as int by default — users migrating existing tables should use Format = "D"
• Best practice guidance on when to use string vs integer (string is safer for refactoring, integer is more compact)