feat: add phase five operations foundation

Tiku.Api/Contracts/BackgroundJobDtos.cs

@@ -0,0 +1,22 @@
+using System.Text.Json;
+using Tiku.Application.Jobs;
+
+namespace Tiku.Api.Contracts;
+
+public sealed class CreateBackgroundJobDto
+{
+    public string JobType { get; set; } = string.Empty;
+    public JsonElement Payload { get; set; }
+    public DateTimeOffset? RunAfter { get; set; }
+    public int MaxRetries { get; set; } = 3;
+
+    public CreateBackgroundJobCommand ToCommand(Guid tenantId)
+    {
+        return new CreateBackgroundJobCommand(
+            tenantId,
+            JobType,
+            Payload.ValueKind == JsonValueKind.Undefined ? JsonSerializer.SerializeToElement(new { }) : Payload,
+            RunAfter,
+            MaxRetries);
+    }
+}