🚚 Rename activity in sphere to timeline

In order to leave the activity keyword for pass service user activity

DysonNetwork.Shared/Models/Timeline.cs

@@ -0,0 +1,41 @@
+using System.ComponentModel.DataAnnotations;
+using System.ComponentModel.DataAnnotations.Schema;
+using NodaTime;
+
+namespace DysonNetwork.Shared.Models;
+
+public interface ITimelineEvent
+{
+    public SnTimelineEvent ToActivity();
+}
+
+[NotMapped]
+public class SnTimelineEvent : ModelBase
+{
+    public Guid Id { get; set; }
+
+    [MaxLength(1024)]
+    public string Type { get; set; } = null!;
+
+    [MaxLength(4096)]
+    public string ResourceIdentifier { get; set; } = null!;
+
+    [Column(TypeName = "jsonb")]
+    public Dictionary<string, object> Meta { get; set; } = new();
+
+    public object? Data { get; set; }
+
+    public static SnTimelineEvent Empty()
+    {
+        var now = SystemClock.Instance.GetCurrentInstant();
+        return new SnTimelineEvent
+        {
+            CreatedAt = now,
+            UpdatedAt = now,
+            Id = Guid.NewGuid(),
+            Type = "empty",
+            ResourceIdentifier = "none",
+        };
+    }
+}
+