feat(worker): expose ResetTask hub method

Wire TaskResetService into DI and add WorkerHub.ResetTask with the
same InvalidOperationException/KeyNotFoundException error-translation
pattern as ContinueTask.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/ClaudeDo.Worker/Program.cs

@@ -30,6 +30,7 @@ builder.Services.AddSingleton<WorktreeManager>();
 builder.Services.AddSingleton<ClaudeArgsBuilder>();
 builder.Services.AddSingleton<TaskRunner>();
 builder.Services.AddSingleton<WorktreeMaintenanceService>();
+builder.Services.AddSingleton<TaskResetService>();
 
 // Agent file management.
 var agentsDir = Path.Combine(ClaudeDo.Data.Paths.AppDataRoot(), "agents");