secret list gives each secret's own creation and last-update times (closes #142)

secret list and secret list --json gave the time of the listing as every
secret's creation and last-update time, because Secret.LoadMetadata set
both to the current time. It now reads file modification times, so
listing still needs no passphrase: the last update is when the secret's
current file was written, and the creation is when its oldest version's
value.age was written. A move to another vault gives the copied files
the times of the originals.

GetSecretObject no longer loads the times, so secret get keeps its error
for a missing current file; secret list calls LoadMetadata itself.

Judgement call: the creation time comes from value.age, not from the
oldest version's directory, whose time changes when the next add
rewrites that version's metadata.age.

Model: opus-5-5

internal/cli/secrets.go

@@ -541,8 +541,12 @@ func printSecretsJSON(
 			"name": secretName,
 		}
 
-		// Try to get metadata using GetSecretObject
+		// A secret whose times cannot be read is listed without them
 		secretObj, err := vlt.GetSecretObject(secretName)
+		if err == nil {
+			err = secretObj.LoadMetadata()
+		}
+
 		if err == nil {
 			metadata := secretObj.GetMetadata()
 			secretInfo["created_at"] = metadata.CreatedAt
@@ -618,6 +622,10 @@ func printSecretsTable(
 		lastUpdated := "unknown"
 
 		secretObj, err := vlt.GetSecretObject(secretName)
+		if err == nil {
+			err = secretObj.LoadMetadata()
+		}
+
 		if err == nil {
 			metadata := secretObj.GetMetadata()
 			lastUpdated = metadata.UpdatedAt.Format("2006-01-02 15:04")