Count every file of each version in secret info's Total Size (closes #147)

Total Size added up each version's data.age and metadata.age, but a
version keeps its value in value.age, so no secret's value was counted.
It now adds up every file in each version directory: the value, the
metadata and the version's two keys, as the plan on the issue decided.
A version directory that cannot be read adds nothing and gets a warning
naming it.

The new tests add a 10000-byte secret and check that the total grows by
at least that much, and check the warning for a version directory that
cannot be read.

Model: opus-5-5

internal/cli/info_helper.go

@@ -18,24 +18,23 @@ type vaultStats struct {
 
 // addVersion accumulates size and timestamp info for one version directory
 func (s *vaultStats) addVersion(fs afero.Fs, versionPath string) {
-	// Add size of encrypted data
-	dataPath := filepath.Join(versionPath, "data.age")
-
-	stat, err := fs.Stat(dataPath)
-	if err == nil {
-		s.totalSize += stat.Size()
+	// Add the size of every file in the version directory: its value,
+	// metadata and keys. A directory that cannot be read adds nothing and
+	// gets a warning; its timestamp is still tracked below.
+	files, err := afero.ReadDir(fs, versionPath)
+	if err != nil {
+		secret.Warn("Could not read version directory",
+			"directory", versionPath, "error", err)
 	}
 
-	// Add size of metadata
-	metaPath := filepath.Join(versionPath, "metadata.age")
-
-	stat, err = fs.Stat(metaPath)
-	if err == nil {
-		s.totalSize += stat.Size()
+	for _, file := range files {
+		if !file.IsDir() {
+			s.totalSize += file.Size()
+		}
 	}
 
 	// Track timestamps
-	stat, err = fs.Stat(versionPath)
+	stat, err := fs.Stat(versionPath)
 	if err == nil {
 		modTime := stat.ModTime()
 		if s.oldestTime.IsZero() || modTime.Before(s.oldestTime) {