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_test.go

@@ -0,0 +1,51 @@
+//nolint:testpackage // white-box test of unexported internals
+package cli
+
+import (
+	"io"
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/spf13/afero"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+// TestAddVersionWarnsWhenVersionDirUnreadable asserts that a version
+// directory that cannot be listed, so that its files are left out of the
+// total size, gets a warning naming it and the error, and that its
+// timestamp is still tracked.
+//
+//nolint:paralleltest // replaces os.Stderr, where secret.Warn writes
+func TestAddVersionWarnsWhenVersionDirUnreadable(t *testing.T) {
+	versionDir := filepath.Join(testVaultDir(listTestVaultName),
+		unreadableTestSecretsDirName, unreadableTestSecretName,
+		"versions", "20260809.001")
+
+	base := afero.NewMemMapFs()
+	require.NoError(t, base.MkdirAll(versionDir, listTestDirPerm))
+
+	stderrReader, stderrWriter, err := os.Pipe()
+	require.NoError(t, err)
+
+	defer func() { _ = stderrReader.Close() }()
+
+	realStderr := os.Stderr
+	os.Stderr = stderrWriter
+
+	var stats vaultStats
+	stats.addVersion(&openFailFs{Fs: base, path: versionDir}, versionDir)
+
+	os.Stderr = realStderr
+
+	require.NoError(t, stderrWriter.Close())
+
+	warning, err := io.ReadAll(stderrReader)
+	require.NoError(t, err)
+
+	assert.Contains(t, string(warning), versionDir)
+	assert.Contains(t, string(warning), errOpenFailed.Error())
+	assert.False(t, stats.latestTime.IsZero(),
+		"the timestamp must still be tracked")
+}