Check vault names in every command that takes one (closes #68)

A vault name may use only lowercase ASCII letters, digits, `.`, `-` and
`_`, and must not be empty, `.` or `..`; the error now states that rule.
`vault create`, `vault import`, `vault select`, `vault remove` and both
vault names of `mv` check the name as typed before building any path
from it. Before, `vault import ..` wrote a long-term key and an unlocker
into the state directory itself, and `vault select ..` made that the
current vault.

Model: opus-5-5

internal/cli/vault.go

@@ -462,6 +462,11 @@ func updateVaultImportMetadata(
 // VaultImport imports a mnemonic into a specific vault, holding the state
 // directory lock while importMnemonic runs
 func (cli *Instance) VaultImport(cmd *cobra.Command, vaultName string) error {
+	err := vault.ValidateVaultName(vaultName)
+	if err != nil {
+		return err
+	}
+
 	release, err := vault.LockStateDir(cli.fs, cli.stateDir)
 	if err != nil {
 		return err
@@ -617,6 +622,11 @@ func (cli *Instance) switchAwayFromVault(
 // RemoveVault removes a vault, holding the state directory lock while
 // removeVault runs
 func (cli *Instance) RemoveVault(cmd *cobra.Command, name string, force bool) error {
+	err := vault.ValidateVaultName(name)
+	if err != nil {
+		return err
+	}
+
 	release, err := vault.LockStateDir(cli.fs, cli.stateDir)
 	if err != nil {
 		return err