feat(gpu): honor device IDs in Docker and Podman

[elezar]

Summary

Honor the existing GPU device ID field for Docker and Podman GPU sandboxes without changing the protobuf API shape.

Related Issue

None.

Changes

• Added a shared helper that maps the existing GPU fields to CDI device IDs.
• Updated Docker device requests to pass explicit GPU device IDs through and keep the default all-GPU CDI request.
• Updated Podman container devices with the same explicit GPU device ID handling.
• Added Rust e2e coverage for Docker and Podman GPU device selection, including default GPU requests, per-index CDI IDs, nvidia.com/gpu=all, and invalid device IDs.
• For per-index CDI selection, the e2e test now verifies the selected physical GPU by UUID because containers may renumber a single visible GPU to ordinal 0.
• Switched the GPU CI workflow from the Python/k3s-oriented GPU suite to the Docker GPU e2e task.
• Repointed e2e:gpu to Docker GPU coverage and kept the previous Python GPU task available as e2e:k3s:gpu.
• Updated Docker and Podman driver documentation notes.
• Fixed the Helm README markdown lint issue that was blocking pre-commit.

Testing

• cargo test --manifest-path e2e/rust/Cargo.toml --features e2e-docker-gpu --test gpu_device_selection --no-run
• cargo test --manifest-path e2e/rust/Cargo.toml --features e2e-podman-gpu --test gpu_device_selection --no-run
• cargo check -p openshell-cli
• git diff --check
• .github/workflows/e2e-gpu-test.yaml YAML parse check
• mise tasks lists e2e:gpu, e2e:k3s:gpu, e2e:docker:gpu, and e2e:python:gpu
• mise run e2e:docker:gpu validated on a dGPU-based system
• mise run markdown:lint:md
• mise run pre-commit
• mise run e2e:podman:gpu still needs to be run

Checklist

• Follows Conventional Commits
• Commits are signed off (DCO)
• Architecture docs updated (if applicable)

[github-actions]

Label test:e2e-gpu applied for 293b1f0. Open the existing run and click Re-run all jobs to execute with the label set. The E2E Gate check on this PR will flip green automatically once the run finishes.