- inherit_parent: true merges a nested config onto the nearest parent config
  (parent is the base, child overrides). A nested config can define just
  remote_path and inherit host/user/password from the parent.
- Without the flag, nested configs stay fully independent (different server).
- Validation runs after the merge; clear error if inherit_parent has no parent.
- Inherited configs are not cached (parent may change independently).
- 'Show Effective Config' now displays the inherited-from parent path.