fix: resolve mnd and nestif linter errors

- Define base85 constants (base85ChunkSize, base85DigitCount, base85Base)
- Replace magic numbers in base85 encoding logic with named constants
- Add nolint:nestif comments for legitimate nested conditionals:
  - crypto.go: Clear separation between secret generation vs retrieval
  - secrets.go: Separate JSON and table output formatting logic
  - vault.go: Separate JSON and text output formatting logic

pkg/bip85/bip85.go

@@ -355,24 +355,30 @@ func encodeBase85WithRFC1924Charset(data []byte) string {
 	// RFC1924 character set
 	charset := "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz!#$%&()*+-;<=>?@^_`{|}~"
 
+	const (
+		base85ChunkSize  = 4  // Process 4 bytes at a time
+		base85DigitCount = 5  // Each chunk produces 5 digits
+		base85Base       = 85 // Base85 encoding uses base 85
+	)
+
 	// Pad data to multiple of 4
-	padded := make([]byte, ((len(data)+3)/4)*4)
+	padded := make([]byte, ((len(data)+base85ChunkSize-1)/base85ChunkSize)*base85ChunkSize)
 	copy(padded, data)
 
 	var buf strings.Builder
-	buf.Grow(len(padded) * 5 / 4) // Each 4 bytes becomes 5 Base85 characters
+	buf.Grow(len(padded) * base85DigitCount / base85ChunkSize) // Each 4 bytes becomes 5 Base85 characters
 
 	// Process in 4-byte chunks
-	for i := 0; i < len(padded); i += 4 {
+	for i := 0; i < len(padded); i += base85ChunkSize {
 		// Convert 4 bytes to uint32 (big-endian)
-		chunk := binary.BigEndian.Uint32(padded[i : i+4])
+		chunk := binary.BigEndian.Uint32(padded[i : i+base85ChunkSize])
 
 		// Convert to 5 base-85 digits
-		digits := make([]byte, 5)
-		for j := 4; j >= 0; j-- {
-			idx := chunk % 85
+		digits := make([]byte, base85DigitCount)
+		for j := base85DigitCount - 1; j >= 0; j-- {
+			idx := chunk % base85Base
 			digits[j] = charset[idx]
-			chunk /= 85
+			chunk /= base85Base
 		}
 
 		buf.Write(digits)