Fix intrange and G101 linting issues

- Convert for loops to use Go 1.22+ integer ranges in generate.go and helpers.go
- Disable G101 false positives for test vectors and environment variable names
- Add file-level gosec disable for bip85_test.go containing BIP85 test vectors
- Add targeted nolint comments for legitimate test data and constants

internal/secret/constants.go

@@ -9,15 +9,15 @@ const (
 	// Environment variable names
 	EnvStateDir         = "SB_SECRET_STATE_DIR"
 	EnvMnemonic         = "SB_SECRET_MNEMONIC"
-	EnvUnlockPassphrase = "SB_UNLOCK_PASSPHRASE"
+	EnvUnlockPassphrase = "SB_UNLOCK_PASSPHRASE" //nolint:gosec // G101: This is an env var name, not a credential
 	EnvGPGKeyID         = "SB_GPG_KEY_ID"
 )
 
 // File system permission constants
 const (
 	// DirPerms is the permission used for directories (read-write-execute for owner only)
-	DirPerms os.FileMode = 0700
+	DirPerms os.FileMode = 0o700
 
 	// FilePerms is the permission used for sensitive files (read-write for owner only)
-	FilePerms os.FileMode = 0600
+	FilePerms os.FileMode = 0o600
 )