feat(worker): add Prime scheduler abstractions + runner

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/ClaudeDo.Worker/Prime/IPrimeRunner.cs

@@ -0,0 +1,8 @@
+namespace ClaudeDo.Worker.Prime;
+
+public interface IPrimeRunner
+{
+    Task<PrimeRunOutcome> FireAsync(PrimeScheduleDto schedule, CancellationToken ct);
+}
+
+public sealed record PrimeRunOutcome(bool Success, string Message);