- 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
- new `orama sandbox reset` deletes Hetzner resources (IPs, firewall, SSH key) and local config
- interactive location/server type selection during `setup`
- add Hetzner API methods for listing locations/types, deleting resources
- update defaults to nbg1/cx23