test(conformance): migrate file transfer coverage

[elezar]

Summary

Move driver-agnostic CLI file-transfer coverage from the Docker Rust E2E suite into reusable conformance scenarios that run against each conformance compute environment.

Stack

1. test(cli): migrate gateway-free smoke coverage #3641 — gateway-free CLI smoke coverage
2. test(conformance): migrate file transfer coverage #3597 — file-transfer conformance coverage
3. test(e2e): run podman suite with tmachine #3637 — Podman E2E tmachine archive

Draft follow-up #3766 branches from this PR for relay reconnect coverage.

Related Issue

No issue required: this is a localized test-suite migration with no user-facing behavior change.

Merge after #3641, which moves gateway-free smoke coverage out of the legacy Rust E2E suite. Relay reconnect regression coverage and its focused fix were split into draft PR #3766.

Changes

• replace e2e/rust/tests/sync.rs with portable file-transfer/{round-trip,git-filtering,path-safety} scenarios
• exercise directory, large-file, and single-file round trips
• verify Git-aware upload filtering and explicit unfiltered fallback behavior
• verify download workspace boundaries and safe handling of special basenames
• install Git in tmachine conformance guests and preserve all test failures
• update conformance architecture guidance

Testing

• mise run pre-commit
• cargo test -p openshell-conformance (18 passed)
• Docker tmachine file-transfer scenarios passed before the rebase
• Rootful Podman tmachine file-transfer scenarios passed before the rebase
• Rootless Podman tmachine file-transfer scenarios passed before the rebase
• Post-rebase GitHub E2E checks

Checklist

• Follows Conventional Commits
• Commits are signed off (DCO)
• Architecture documentation updated

[github-actions]

Label test:e2e applied for bc8109d. Open the existing run and click Re-run all jobs to execute with the label set. The run will execute the standard E2E suite after building the required gateway, sandbox, and supervisor images once. The matching required CI gate status on this PR will flip green automatically once the run finishes.

[elezar]

/ok to test bc8109d