v2 CLI `resource-group get` fails with ValidationError due to DTO schema mismatch

Running `./bai resource-group get default` crashes with a Pydantic `ValidationError` containing 7 field errors.

The REST API response does not match the `ResourceGroupNode` DTO:

- `id` is returned as the name string (`"default"`) instead of a UUID

- Required fields `domain_name`, `is_active`, `total_resource_slots`, `allowed_vfolder_hosts`, `created_at`, `modified_at` are missing from the response

Steps to reproduce:

1. `./bai resource-group get default`

Expected: Resource group details displayed

Actual: `pydantic_core._pydantic_core.ValidationError: 7 validation errors for ResourceGroupNode`

Root cause: The REST v2 handler for `resource-group get` returns a different response shape than what `ResourceGroupNode` expects. Either the handler needs to include all required fields, or the DTO needs to align with the actual response.

JIRA Issue: BA-5642