fix: resolve gochecknoglobals, gosec, lll, and mnd linter errors

- Add nolint comments for BIP85 standard constants (MainNetPrivateKey, TestNetPrivateKey)
- Handle error return from shake.Write() in NewBIP85DRNG
- Fix line length issue by moving nolint comment to separate line
- Add nolint comment for cobra.ExactArgs(2) magic number
- Replace magic number 32 with named constant x25519KeySize in agehd package

pkg/bip85/bip85.go

@@ -40,9 +40,9 @@ const (
 // Version bytes for extended keys
 var (
 	// MainNetPrivateKey is the version for mainnet private keys
-	MainNetPrivateKey = []byte{0x04, 0x88, 0xAD, 0xE4}
+	MainNetPrivateKey = []byte{0x04, 0x88, 0xAD, 0xE4} //nolint:gochecknoglobals // Standard BIP32 constant
 	// TestNetPrivateKey is the version for testnet private keys
-	TestNetPrivateKey = []byte{0x04, 0x35, 0x83, 0x94}
+	TestNetPrivateKey = []byte{0x04, 0x35, 0x83, 0x94} //nolint:gochecknoglobals // Standard BIP32 constant
 )
 
 // DRNG is a deterministic random number generator seeded by BIP85 entropy
@@ -59,7 +59,7 @@ func NewBIP85DRNG(entropy []byte) *DRNG {
 
 	// Initialize SHAKE256 with the entropy
 	shake := sha3.NewShake256()
-	shake.Write(entropy)
+	_, _ = shake.Write(entropy) // Write to hash functions never returns an error
 
 	return &DRNG{
 		shake: shake,