fix(compose): strip and resolve pre-deploy hook secrets like service env (#424)

* fix(compose): strip and resolve pre-deploy hook secrets like service env (fixes #422)

normaliseContainerForStore only cleared Config.Env and
ServiceSpec.Container.Env before writing a container record to the
replicated Corrosion store, leaving ServiceSpec.PreDeploy.Env in place.
A secret set via x-pre_deploy.environment therefore replicated to
every machine in the cluster, unlike the same value set via
environment.

ResolveSecrets had the same asymmetry in the other direction: it only
resolved secret://name references in service.Environment, so a
reference placed in the pre-deploy hook's environment passed through
unresolved as a literal string. HasCommandSecretRefs is extended the
same way for consistency.

Add tests pinning both behaviours.

* update docs that secret references are available for pre-deploy hooks

---------

Co-authored-by: Pasha Sviderski <me@psviderski.name>

internal/machine/store/container.go

@@ -96,6 +96,9 @@ func normaliseContainerForStore(ctr *api.ServiceContainer) {
 	// Remove the environment variables to avoid leaking secrets.
 	ctr.Config.Env = nil
 	ctr.ServiceSpec.Container.Env = nil
+	if ctr.ServiceSpec.PreDeploy != nil {
+		ctr.ServiceSpec.PreDeploy.Env = nil
+	}
 
 	// Docker returns Mounts in a non-deterministic order so sort them.
 	slices.SortFunc(ctr.Mounts, func(a, b container.MountPoint) int {