feat(pod): add spot pod support with --bid-per-gpu flag

[TimPietruskyRunPod]

Summary

The new pod create command (v2.0.0) has no way to create spot instances. The old deprecated start pod command supported this via --bid and the podRentInterruptable GraphQL mutation, but that code path is deprecated.

Desired behavior

runpodctl pod create --template-id <id> --gpu-id "NVIDIA RTX 4090" --bid-per-gpu 0.20

When --bid-per-gpu is provided, use the podRentInterruptable mutation instead of podFindAndDeployOnDemand.

Reference

PR #186 implemented this for the legacy CLI — see the approach there for the GraphQL mutation and flag handling. Key pieces:

• bidPerGpu field in the GraphQL input
• podRentInterruptable mutation
• Validation: bid must be > 0

Files to modify

• cmd/pod/create.go — add --bid-per-gpu flag
• internal/api/graphql.go — add podRentInterruptable mutation support