Reject invalid secret names before any command builds a path (closes #33)

`secret rm ..` resolved to the vault directory and deleted the whole
vault; `secret rm .` and `secret rm ""` deleted every secret. rm, mv,
the version commands, encrypt and decrypt built paths from the name
without checking it; import checked it only after reading the source
file.

vault.ValidateSecretName wraps the existing name rule and its error
states the rule. Each of those commands calls it on the name as given,
before building any path; a move checks both names before switching
the current vault. AddSecret, GetSecretVersion and GetSecretObject use
it too.

The regression test copies two in-memory vaults for each rejected
command and requires the exact error and an unchanged state directory.

Model: opus-5-5

internal/cli/secrets.go

@@ -603,6 +603,11 @@ func printSecretsTable(
 func (cli *Instance) ImportSecret(
 	cmd *cobra.Command, secretName, sourceFile string, force bool,
 ) error {
+	err := vault.ValidateSecretName(secretName)
+	if err != nil {
+		return err
+	}
+
 	// Get current vault
 	vlt, err := vault.GetCurrentVault(cli.fs, cli.stateDir)
 	if err != nil {
@@ -649,6 +654,11 @@ func (cli *Instance) ImportSecret(
 
 // RemoveSecret removes a secret from the vault
 func (cli *Instance) RemoveSecret(cmd *cobra.Command, secretName string, _ bool) error {
+	err := vault.ValidateSecretName(secretName)
+	if err != nil {
+		return err
+	}
+
 	// Get current vault
 	currentVlt, err := vault.GetCurrentVault(cli.fs, cli.stateDir)
 	if err != nil {
@@ -737,10 +747,22 @@ func (cli *Instance) MoveSecret(
 		destSecretName = srcSecretName
 	}
 
+	// Check both names before selecting a vault below, so that a rejected
+	// move leaves the current vault as it was.
+	err := vault.ValidateSecretName(srcSecretName)
+	if err != nil {
+		return err
+	}
+
+	err = vault.ValidateSecretName(destSecretName)
+	if err != nil {
+		return err
+	}
+
 	// Same vault? Use simple rename if possible (optimization)
 	if srcVaultName == destVaultName {
 		// Select the vault and do a simple move
-		err := vault.SelectVault(cli.fs, cli.stateDir, srcVaultName)
+		err = vault.SelectVault(cli.fs, cli.stateDir, srcVaultName)
 		if err != nil {
 			return fmt.Errorf("failed to select vault '%s': %w", srcVaultName, err)
 		}
@@ -757,6 +779,16 @@ func (cli *Instance) MoveSecret(
 func (cli *Instance) moveSecretWithinVault(
 	cmd *cobra.Command, source, dest string, force bool,
 ) error {
+	err := vault.ValidateSecretName(source)
+	if err != nil {
+		return err
+	}
+
+	err = vault.ValidateSecretName(dest)
+	if err != nil {
+		return err
+	}
+
 	currentVlt, err := vault.GetCurrentVault(cli.fs, cli.stateDir)
 	if err != nil {
 		return err
@@ -808,7 +840,8 @@ func (cli *Instance) moveSecretWithinVault(
 	return nil
 }
 
-// moveSecretCrossVault handles moving between different vaults
+// moveSecretCrossVault handles moving between different vaults. Its caller,
+// MoveSecret, has already checked both secret names.
 func (cli *Instance) moveSecretCrossVault(
 	cmd *cobra.Command,
 	srcVaultName, srcSecretName,