- replace `rw vault ssh` calls with `rwagent.Client` in PrepareNodeKeys,
LoadAgentKeys, EnsureVaultEntry, ResolveVaultPublicKey
- add vaultClient interface, newClient func, and wrapAgentError for
testability and improved error messages
- prefer pre-built systemd dir in installNamespaceTemplates
- replace standalone sandbox keys with "sandbox/root" vault entry
- update inspector config to use vault targets (no passwords/keys)
- make sandbox default active environment
- add vault helpers and tests for remotessh
- add WithNoHostKeyCheck option for ephemeral server IPs
- upload binary to genesis then distribute to other nodes (faster)
- improve provisioning error handling for cleanup on partial failure