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/agehd/agehd.go

@@ -37,7 +37,8 @@ func clamp(k []byte) {
 // IdentityFromEntropy converts 32 deterministic bytes into an
 // *age.X25519Identity by round-tripping through Bech32.
 func IdentityFromEntropy(ent []byte) (*age.X25519Identity, error) {
-	if len(ent) != 32 { // 32 bytes = 256-bit key size for X25519
+	const x25519KeySize = 32 // 256-bit key size for X25519
+	if len(ent) != x25519KeySize {
 		return nil, fmt.Errorf("need 32-byte scalar, got %d", len(ent))
 	}