Create a new public Google Calendar.
```bash
rscalendar calendar create <NAME>
```
Creates a new calendar with the given name and sets it to public (readable by anyone). The calendar ID is printed on success — use it with `--calendar-id` or in `config.toml`.
```bash
$ rscalendar calendar create Teaching
Created public calendar 'Teaching'
id: abc123@group.calendar.google.com
```