test(conformance): migrate create-upload tests to file_transfer stories

[politerealism]

Summary

Move the three sandbox create --upload tests from the legacy Podman e2e crate into the file_transfer conformance area as story modules. The behavior isn't Podman-specific, so it belongs with the other file transfer stories and runs against any prepared gateway. Stacked on #4538, which relocates the suites.

Related Issue

Contributes to #3954. No separate issue: this migrates existing coverage.

Changes

• Add file_transfer/create_upload.rs with three stories, keeping the original test names so filters keep working: create_with_upload_directory_preserves_source_basename, create_with_multiple_uploads and create_with_upload_single_file.
• Verify uploads by reading files back with sandbox exec and comparing exact content. The originals matched the printed output of sandbox create.
• Check the nested file in the directory story, and that the directory isn't flattened into the destination. Check each destination separately in the multiple-uploads story.
• Use the default upload path. The originals passed --no-git-ignore, which isn't needed outside a Git work tree and hid the default path.
• Create the sandbox from the target's default image, as the README expects. The originals used the e2e test image.
• Drop the claim that files arrive before the command runs. The CLI rejects --upload together with a command, and the docs say uploads finish after the main process starts, so each story checks the files once create returns, and the module doc notes the limitation.
• Delete e2e/rust/tests/upload_create.rs and the now-unused SandboxGuard::create_with_upload and create_with_uploads from the legacy harness.

Testing

• mise run pre-commit passes
• All six file_transfer tests (these three and the three existing ones) pass against a rootless Podman gateway: cargo test --manifest-path e2e/suites/conformance/Cargo.toml --test file_transfer
• All five e2e feature sets (e2e, e2e-podman, e2e-docker, e2e-kubernetes, e2e-vm) still compile without warnings
• Deliberate-failure checks on the same gateway, each failing exactly the intended story: wrong directory content, the not-flattened check inverted, wrong second-upload content, and wrong single-file content.
• tmachine guests, run on a throwaway branch that combines the three migrations: the full conformance archive passes in the Ubuntu rootful Docker guest (tmachine test ubuntu-docker-rootful binaries conformance) and in the Ubuntu K3s guest (tmachine test ubuntu-k3s k3s conformance). The first Docker run is what exposed the provider-profile dependency fixed in the workspaces PR, and it also failed once on the existing lifecycle stop_start (ContainerExited: Container exited while waiting for Ready), which passed on the rerun. Each PR alone was not run in tmachine.
• Not run: macOS.

Checklist

• Follows Conventional Commits
• Commits are signed off (DCO)
• Architecture docs updated (not applicable)

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