feat(uhost): enrich GPU creation in uhost create

- Expand --gpu-type values from 3 (K80/P40/V100) to 31 to align with
  API GpuConfigs.SeriesID (T4, 4090, H100, 5090Pro, etc.)
- Add mutual-required validation: --gpu requires --gpu-type and vice
  versa, preventing silent creation of non-GPU instances when only
  one is specified
- Auto-set MachineType to G when both --gpu and --gpu-type are
  provided, unless user explicitly sets --machine-type
- Change --machine-type default from N to O