feat(worker): add WorktreeMaintenanceService for idle-worktree cleanup

src/ClaudeDo.Worker/Program.cs

@@ -29,6 +29,7 @@ builder.Services.AddSingleton<GitService>();
 builder.Services.AddSingleton<WorktreeManager>();
 builder.Services.AddSingleton<ClaudeArgsBuilder>();
 builder.Services.AddSingleton<TaskRunner>();
+builder.Services.AddSingleton<WorktreeMaintenanceService>();
 
 // Agent file management.
 var agentsDir = Path.Combine(ClaudeDo.Data.Paths.AppDataRoot(), "agents");