fix: resolve errcheck, gosec, and mnd linter errors

- Fixed unhandled errors in init.go (os.Setenv/Unsetenv)
- Fixed unhandled errors in test_helpers.go (os.Setenv/Unsetenv)
- Replaced magic numbers with named constants:
  - defaultSecretLength = 16
  - mnemonicEntropyBits = 128
  - tabWriterPadding = 2

internal/cli/generate.go

@@ -11,6 +11,11 @@ import (
 	"github.com/tyler-smith/go-bip39"
 )
 
+const (
+	defaultSecretLength = 16
+	mnemonicEntropyBits = 128
+)
+
 func newGenerateCmd() *cobra.Command {
 	cmd := &cobra.Command{
 		Use:   "generate",
@@ -55,7 +60,7 @@ func newGenerateSecretCmd() *cobra.Command {
 		},
 	}
 
-	cmd.Flags().IntP("length", "l", 16, "Length of the generated secret (default 16)")
+	cmd.Flags().IntP("length", "l", defaultSecretLength, "Length of the generated secret (default 16)")
 	cmd.Flags().StringP("type", "t", "base58", "Type of secret to generate (base58, alnum)")
 	cmd.Flags().BoolP("force", "f", false, "Overwrite existing secret")
 
@@ -65,7 +70,7 @@ func newGenerateSecretCmd() *cobra.Command {
 // GenerateMnemonic generates a random BIP39 mnemonic phrase
 func (cli *Instance) GenerateMnemonic(cmd *cobra.Command) error {
 	// Generate 128 bits of entropy for a 12-word mnemonic
-	entropy, err := bip39.NewEntropy(128)
+	entropy, err := bip39.NewEntropy(mnemonicEntropyBits)
 	if err != nil {
 		return fmt.Errorf("failed to generate entropy: %w", err)
 	}