Add scene graph draft

Ghost.Editor.Core/Serialization/SceneData.cs

@@ -0,0 +1,66 @@
+using System.Text.Json.Serialization;
+
+namespace Ghost.Editor.Core.Serialization;
+
+/// <summary>
+/// Represents the serialized data for a scene in JSON format.
+/// This is editor-only and used for scene file persistence.
+/// </summary>
+public class SceneData
+{
+    /// <summary>
+    /// The name of the scene.
+    /// </summary>
+    [JsonPropertyName("name")]
+    public string Name { get; set; } = "New Scene";
+
+    /// <summary>
+    /// List of entities in this scene, ordered by file-local ID.
+    /// The index in this list IS the file-local ID.
+    /// </summary>
+    [JsonPropertyName("entities")]
+    public List<EntityData> Entities { get; set; } = [];
+}
+
+/// <summary>
+/// Represents the serialized data for an entity.
+/// </summary>
+public class EntityData
+{
+    /// <summary>
+    /// The display name of this entity (editor-only).
+    /// </summary>
+    [JsonPropertyName("name")]
+    public string Name { get; set; } = "Entity";
+
+    /// <summary>
+    /// The file-local ID of the parent entity, or -1 if root.
+    /// </summary>
+    [JsonPropertyName("parent")]
+    public int ParentLocalId { get; set; } = -1;
+
+    /// <summary>
+    /// Dictionary of component data, keyed by component type name.
+    /// </summary>
+    [JsonPropertyName("components")]
+    public Dictionary<string, ComponentData> Components { get; set; } = [];
+}
+
+/// <summary>
+/// Represents the serialized data for a component.
+/// </summary>
+public class ComponentData
+{
+    /// <summary>
+    /// The component type full name (for deserialization).
+    /// </summary>
+    [JsonPropertyName("type")]
+    public string TypeName { get; set; } = "";
+
+    /// <summary>
+    /// The serialized component fields.
+    /// Entity references are stored as file-local IDs (integers).
+    /// </summary>
+    [JsonPropertyName("fields")]
+    public Dictionary<string, object?> Fields { get; set; } = [];
+}