- Rename VaultMetadata to Metadata in internal/vault package to avoid stuttering
- Rename BIP85DRNG to DRNG in pkg/bip85 package to avoid stuttering
- Update all references in code and tests
Replace hardcoded 0o600 with secret.FilePerms constant for consistency.
Add explanatory comments for cryptographic constants (32-byte keys,
bech32 encoding parameters) rather than extracting them as they are
well-known cryptographic standard values.
