Release v0.1.5

Adds sparrow_engine.__version__ + README uv-venv install fix.

See sparrow-engine-dev docs/changelog.md § 2026-05-26 (PM, +2) for the
forensics + verification record.

feat(phase-h): enable prod-PyPI GPU publish + bump to 0.1.4

Phase H deliverable: flip `publish-pypi-gpu` from `if: false` to the
same tag-push gate as `publish-pypi-cpu` (only on non-prerelease version
tags), and add the mirrored "Validate tag matches wheel version" step
to enforce the PyPI immutability invariant on the GPU side.

Version bump 0.1.3 -> 0.1.4 for the first production PyPI release.
0.1.3 stays as the last TestPyPI-only build (Phase F sign-off).

Trusted publishers on prod PyPI already claimed for both
`sparrow-engine` and `sparrow-engine-gpu` per user confirmation
2026-05-25 22:14 PT.

Files:
- .github/workflows/release.yml: flip GPU prod-publish gate +
  add tag-version validation step + update header comment block
- sparrow-engine/sparrow-engine-python/pyproject.toml: 0.1.3 -> 0.1.4
- sparrow-engine/sparrow-engine-python/Cargo.toml: 0.1.3 -> 0.1.4
- sparrow-engine/Cargo.lock: regenerated via `cargo update -p sparrow-engine-python`

Dry-run plan: `gh workflow run release.yml -r phase-h-pypi-prod-publish -f target=testpypi`
verifies both 0.1.4 wheels land on TestPyPI before the real tag push
triggers the prod publish.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>