Switch from relative paths to bare names in pointer files

- currentvault now contains just the vault name (e.g., "default")
- current-unlocker now contains just the unlocker name (e.g., "passphrase")
- current version file now contains just the version (e.g., "20231215.001")
- Resolution functions prepend the appropriate directory prefix

internal/secret/secret_test.go

@@ -101,10 +101,9 @@ func (m *MockVault) AddSecret(name string, value *memguard.LockedBuffer, _ bool)
 		return err
 	}
 
-	// Create current symlink pointing to the version
+	// Create current file pointing to the version (just the version name)
 	currentLink := filepath.Join(secretDir, "current")
-	// For MemMapFs, write a file with the target path
-	if err := afero.WriteFile(m.fs, currentLink, []byte("versions/"+versionName), 0o600); err != nil {
+	if err := afero.WriteFile(m.fs, currentLink, []byte(versionName), 0o600); err != nil {
 		return err
 	}