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/test_helpers.go

@@ -20,7 +20,7 @@ func ExecuteCommandInProcess(args []string, stdin string, env map[string]string)
 
 	// Set test environment
 	for k, v := range env {
-		os.Setenv(k, v)
+		_ = os.Setenv(k, v)
 	}
 
 	// Create root command
@@ -53,9 +53,9 @@ func ExecuteCommandInProcess(args []string, stdin string, env map[string]string)
 	// Restore environment
 	for k, v := range savedEnv {
 		if v == "" {
-			os.Unsetenv(k)
+			_ = os.Unsetenv(k)
 		} else {
-			os.Setenv(k, v)
+			_ = os.Setenv(k, v)
 		}
 	}