fix: resolve mnd and nestif linter errors

- Added constants to replace magic numbers:
  - agePrivKeyPassphraseLength = 64
  - versionNameParts = 2
  - maxVersionsPerDay = 999
- Refactored crypto.go to reduce nesting complexity:
  - Inverted if condition to handle non-existent secret first
  - Extracted getSecretValue helper method

internal/secret/version.go

@@ -15,6 +15,11 @@ import (
 	"github.com/spf13/afero"
 )
 
+const (
+	versionNameParts  = 2
+	maxVersionsPerDay = 999
+)
+
 // VersionMetadata contains information about a secret version
 type VersionMetadata struct {
 	ID        string     `json:"id"`                  // ULID
@@ -87,7 +92,7 @@ func GenerateVersionName(fs afero.Fs, secretDir string) (string, error) {
 		if entry.IsDir() && strings.HasPrefix(entry.Name(), prefix) {
 			// Extract serial number
 			parts := strings.Split(entry.Name(), ".")
-			if len(parts) == 2 {
+			if len(parts) == versionNameParts {
 				var serial int
 				if _, err := fmt.Sscanf(parts[1], "%03d", &serial); err == nil {
 					if serial > maxSerial {
@@ -100,7 +105,7 @@ func GenerateVersionName(fs afero.Fs, secretDir string) (string, error) {
 
 	// Generate new version name
 	newSerial := maxSerial + 1
-	if newSerial > 999 {
+	if newSerial > maxVersionsPerDay {
 		return "", fmt.Errorf("exceeded maximum versions per day (999)")
 	}