Say what each command needs in --help and config.example.yml

snapshot verify --help now says --deep needs the age private key, from
VAULTIK_AGE_SECRET_KEY or age_secret_key, as snapshot restore does.
Both now name the config key as well as the environment variable.

The help of snapshot create, list, purge, remove, prune, remote info
and remote nuke says which access to the destination it needs.
config.example.yml gains age_secret_key, and no longer tells the reader
to pipe age-keygen into grep, which discards the private key.

Only help strings and comments change.

Model: fable-5-1

internal/cli/remote.go

@@ -40,11 +40,13 @@ func newRemoteNukeCommand() *cobra.Command {
 	cmd := &cobra.Command{
 		Use:   "nuke",
 		Short: "Delete ALL snapshot metadata and blobs from the backup destination store",
-		Long: `Removes every snapshot's metadata and every blob from remote
-storage. After this command completes successfully the bucket prefix is
+		Long: `Removes every snapshot's metadata, every blob and the destination
+marker from remote storage, and each removed snapshot from the local
+index. After this command completes successfully the bucket prefix is
 empty and the next backup starts from scratch.
 
-This is destructive and irreversible. Requires --force.`,
+This is destructive and irreversible. Requires --force, and permission
+to list and delete objects on the destination store.`,
 		Args: cobra.NoArgs,
 		RunE: func(cmd *cobra.Command, _ []string) error {
 			if !force {
@@ -75,7 +77,10 @@ func newRemoteInfoCommand() *cobra.Command {
 - Size of all snapshot metadata (per snapshot and total)
 - Count and total size of all blobs
 - Count and size of referenced blobs (from all manifests)
-- Count and size of orphaned blobs (not referenced by any manifest)`,
+- Count and size of orphaned blobs (not referenced by any manifest)
+
+Needs permission to list and read the destination store. It does not
+need the age private key.`,
 		Args: cobra.NoArgs,
 		RunE: func(cmd *cobra.Command, _ []string) error {
 			// Use unified config resolution