Fix vault creation to require mnemonic and set up initial unlocker

- Vault creation now prompts for mnemonic if not in environment
- Automatically creates passphrase unlocker during vault creation
- Prevents 'missing public key' error when adding secrets to new vaults
- Updates tests to reflect new vault creation flow

internal/cli/root.go

@@ -42,6 +42,7 @@ func newRootCmd() *cobra.Command {
 	cmd.AddCommand(newDecryptCmd())
 	cmd.AddCommand(newVersionCmd())
 	cmd.AddCommand(newInfoCmd())
+	cmd.AddCommand(newCompletionCmd())
 
 	secret.Debug("newRootCmd completed")