fix(hub): stop launching system updaters after manager shutdown (#1950) (#1951)

The staggered Initialize goroutine kept calling AddSystem after the hub
had been torn down, which spawned StartUpdater goroutines that later
dereferenced a nil DB inside PocketBase. Track a manager-level context
that RemoveAllSystems cancels, abort the staggered loop on shutdown,
and refuse AddSystem once the manager is stopped.

internal/hub/systems/systems_test_helpers.go

@@ -111,6 +111,11 @@ func (sm *SystemManager) SetSystemStatusInDB(systemID string, status string) boo
 
 // TESTING ONLY: RemoveAllSystems removes all systems from the store
 func (sm *SystemManager) RemoveAllSystems() {
+	// Signal shutdown first so any in-flight Initialize staggered-start goroutine
+	// stops adding new systems against a hub that is about to be torn down. See #1950.
+	if sm.cancel != nil {
+		sm.cancel()
+	}
 	for _, system := range sm.systems.GetAll() {
 		sm.RemoveSystem(system.Id)
 	}