TaskRegistry.CreateSingletonTask delegates to ResourceManager.RegisterBackgroundTask
and stores the task in the ResourceManager's registry, not TaskRegistry.tasks.
TaskRegistry.StopAllTasks previously iterated its own (always-empty) registry,
silently leaking every process-global singleton task's ticker goroutine past the
last Close (memory-monitor, replay-cache-cleanup) — tasks kept running real
periodic work with no instance to serve.
Add ResourceManager.StopAllTasks (stops all rm-owned tasks) and have
TaskRegistry.StopAllTasks stop both its own RegisterTask-direct tasks and the
ResourceManager-owned singletons.
Regression TestR88StopAllTasksStopsResourceManagerOwnedTasks (review_r88_test.go):
fails on old code (task still running after StopAllTasks), passes on new.
