GitVaulty 4.2.0

• Restore full recipient registry v3 support across the CLI, VS Code extension, and JetBrains
  plugin while preserving v3 on every normal write.
• Add gitvaulty registry upgrade --check and an explicit, verified v3-to-v4 migration that
  replaces public identities, signs group policies, and re-encrypts affected ciphertext.
• Show a non-blocking registry upgrade notice once per clone. Unknown future registry versions
  continue to fail closed.