- tools/nidusctl: subcommands `calendar {share,unshare,shares}` and
`addressbook {share,unshare,shares}`, thin wrapper around internal/db.
Warns (non-fatal) if owner/user isn't in config.yaml.
- internal/db: add SharesOfAddressBook (owner-perspective query, mirrors
SharesOfCalendar) needed by the CLI.
- internal/db: db.Open now creates the parent data directory itself, so
the CLI works standalone without requiring the server to have run first.
- Update Makefile (build bin/nidusctl, new 'nidusctl' target), README and
copilot-instructions with usage docs.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>