Clean up admin CLI commands to simplify url parameter passing

[allenporter]

Currently, the admin CLI commands in supernote/cli/admin.py pass the url parameter around through several function calls (e.g., list_users_async, add_user_async, reset_password_async, queue_status_async, etc.) to support the global --url override flag.

This leads to unnecessary boilerplate and verbose function signatures. We should clean this up and simplify the codebase, perhaps by:

1. Managing the active URL context globally or storing it in a config/session context.
2. Modifying the create_session context manager / load_cached_auth helper to automatically retrieve the active override URL from the argparse execution context so subcommands don't need to explicitly accept and pass the url parameter down.