[codex] Add cross-platform release QA coverage

[vkehfdl1]

Summary

• add native OS Rust CI matrix plus CLI and strategy smoke jobs
• add reusable CLI, strategy, and release metadata preflight scripts
• add Python release wheel import smoke coverage and release preflight gates

Verification

• cargo fmt --check
• cargo clippy --workspace -- -D warnings
• cargo test --workspace
• python3 -m pytest -q crates/agentdir/tests/issue_18_release_qa.py
• python3 scripts/ci/release_preflight.py --metadata-only
• python3 scripts/ci/cli_smoke.py --agentdir target/debug/agentdir
• python3 scripts/ci/strategy_smoke.py --agentdir target/debug/agentdir
• act pull_request -W .github/workflows/ci.yml -j rust --matrix os:ubuntu-latest --container-architecture linux/amd64

Notes

Native macOS and Windows runner execution cannot be reproduced on this local macOS host; the workflow now delegates those checks to GitHub Actions on macos-latest and windows-latest.